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Water Quality  Glossary

A Dictionary of Technical and Legal Terms Related to Water


absorbed dose. The amount of a chemical that enters the body of an exposed organism.

absorption. The uptake of water or dissolved chemicals by a

cell or an organism (as tree roots absorb dissolved nutrients

in the soil).

absorption factor. The fraction of a chemical making contact

with an organism that is absorbed by the organism.

acceptable daily Intake (ADI). Estimate of the largest amount

of chemical to which a person can be exposed on a daily basis

that is not anticipated to result in adverse effects

(usually expressed in mg/kg/day). Same as RfD.

accuracy. How closely an instrument measures the true or

actual value of the process variable being measured or sensed.

acid mine drainage. Drainage of water from areas that have

been mined for coal of other mineral ores; the water has

low pH, sometimes less than 2.0 (is acid), because of its

contact with sulfur-bearing material; acid drainage is harmful

because it often kills aquatic organisms.

acid rain. Precipitation which has been rendered (made)

acidic by airborne pollutants.

acidic (uh-SID-ick). The condition of water or soil which

contains a sufficient amount of acid substances to lower the

pH below 7.0.

acidified (uh-SID-uh-FIE-d). The addition of an acid

(usually nitric or sulfuric) to a sample to lower the pH

below 2.0. The purpose of acidification is to "fix" a sample

so it won't change until it is analyzed.

acre-foot A volume of water that covers one acre to a depth

of one foot, or 43,560 cubic feet (1233.5 cubic meters).

activated carbon. Adsorptive particles or granules of carbon

usually obtained by heating carbon (such as wood). These

particles or granules have a high capacity to selectively

remove certain trace and soluble materials from water.

active transport. An energy-expending mechanism by which

a cell moves a chemical across the cell membrane from a

point of lower concentration to a point of higher concentra-

tion, against the diffusion gradient.

action level. The concentration of lead or copper in water

specified at Code of Federal Regulations 141.80(c) which

determines, in some cases, the treatment requirements

contained in subpart I of this part that a water system is

required to complete.

acute. Occurring over a short period of time; used to describe

brief exposures and effects which appear promptly after exposure.

acute exposure. A single exposure to a toxic substance which

results in severe biological harm or death. Acute exposures

are usually characterized as lasting no longer than a day.

acute toxicity. The ability of a substance to cause poisonous

effects resulting in severe biological harm or death soon

after a single exposure or dose. Also, any severe poisonous

effect resulting from a single short-term exposure to a toxic


additive effect. Combined effect of two or more chemicals

equal to the sum of their individual effects.

adsorbate (add-SORE-bait). The material being removed by

the adsorption process.

adsorbent (add-SORE-bent). The material (activated

carbon) that is responsible for removing the undesirable

substance in the adsorption process.

adsorption. The process by which chemicals are held on the

surface of a mineral or soil particle (compare with Absorption).

aeration (air-A-shun). The process of adding air to water.

Air can be added to water by either passing air through

water or passing water through air.

aerobic (air-0-bick). A condition in which free" (atmo-

spheric) or dissolved oxygen is present in the water.

age tank. A tank used to store a chemical solution of known

concentration for feed to a chemical feeder. Also called a

day tank.

aggregate. A mass or cluster of soil particles, often having a

characteristic shape.

agrochemical. Synthetic chemicals (pesticide and fertilizers)

used in agricultural production.

air binding. A situation where air enters the filter media. Air

is harmful to both the filtration and backwash processes. Air

can prevent the passage of water during the filtration

process and can cause the loss of filter media during the

backwash process.

air gap. An open vertical drop, or vertical empty space, that

separates a drinking (potable) water supply to be protected

from another water system in a water treatment plant or

other location. This open gap prevents the contamination of

drinking water by backsiphonage or backflow because there

is no way raw water or any other water can reach the

drinking water.

air padding. Pumping dry air into a container to assist with

the withdrawal of a liquid or to force a liquefied gas such as

chlorine out of a container.

air stripping. A treatment process used to remove dissolved

gases and volatile substances from water. Large volumes of

air are bubbled through the water being treated to remove

(strip out) the dissolved gases and volatile substances. Also

see packed tower aeration.

alarm contact. A switch that operates when some pre-set

low, high or abnormal condition exists.

algae. Microscopic plants which contain chlorophyll and live

floating or suspended in water. They also may be attached

to structures, rocks or other submerged surfaces. They are

food for fish and small aquatic animals. Excess algal

growths can impart tastes and odors to potable water. Algae

produce oxygen during sunlight hours and use oxygen

during the night hours. Their biological activities apprecia-

bly affect the pH and dissolved oxygen of the water.

algal bloom (AL-gull). Sudden, massive growths of micro-

scopic and macroscopic plant life, such as green or blue-

green algae, which develop in lakes and reservoirs.

algicide (AL-gi-SIDE). Any substance or chemical specifi-

cally formulated to kill or control algae.

aliphatic hydroxy acids (Al-uh-FAT-ick). Organic acids

with carbon atoms arranged in branched or unbranched

open chains rather than in rings.

aliquot (AL-li-kwot). Portion of a sample.

alkali (AL-ka-lie). Various soluble salts, principally of

sodium, potassium, magnesium, and calcium, that have the

property of combining with acids to form neutral salts and

may be used in chemical water treatment processes.

alkaline (Al-ka-LINE). The condition of water or soil which

contains a sufficient amount of alkali substances to raise the

pH above 7.0.

alkalinity (AL-ka-LIN-it-tee). The capacity of water to

neutralize acids. This capacity is caused by the water's

content of carbonate, bicarbonate, hydroxide and occasion-

ally borate, silicate, and phosphate. Alkalinity is expressed

in milligrams per liter of equivalent calcium carbonate.

Alkalinity is not the same as pH because water does not

have to be strongly basic (high pH) to have a high alkalin-

ity. Alkalinity is a measure of how much acid can be added

to a liquid without causing a great change in pH.

alluvial (uh-LOU-vee-ul). Relating to mud and/or sand

deposited by flowing water. Alluvial deposits may occur

after a heavy rain storm.

alternating current (A.C.). An electric current that reverses

its direction (positive/negative values) at regular intervals.

ambient. Environmental or surrounding conditions.

ambient temperature (AM-bee-ent). Temperature of the

surrounding air (or other medium). For example, tempera-

ture of the room where a gas chlorinator is installed.

ammonium. One form of nitrogen that is usable by plants.

amperage (AM-purr-age). The strength of an electric

current measured in amperes. The amount of electric

current flow, similar to the flow of water in gallons per


ampere (AM-peer). The unit used to measure current strength.

The current produced by electromotive force of one volt

acting through a resistance of one ohm

amperometric (am-PURR-o-MET-rick). Based on the

electric current that flows between two electrodes in a


amperometric titration. A means of measuring concentra-

tions of certain substances in water (such as strong oxidiz-

ers) based on the electric current that flows during a

chemical reaction. See titrate.

anaerobic (AN-air-O-bick). A condition in which "free"

(atmospheric) or dissolved oxygen is NOT present in water.

analog. The readout of an instrument by a pointer (or other

indicating means) against a dial or scale.

analyzer. A device which conducts periodic or continuous

measurement of some factor such as chlorine, fluoride or

turgidity. Analyzers operate by any of several methods

including photocells, conductivity or complex instrumenta-


animal studies. Investigations using animals as surrogates for

humans, on the expectation that results in animals are

pertinent to humans.

anion (AN-EYE-en). A negatively charged ion in an

electrolyte solution, attracted to the anode under the

influence of a difference in electrical potential. Chloride

(CI-) is an anion.

anionic polymer (AN-eye-ON-ick). A polymer having

negatively charged groups of ions; often used as a filter aid

and for dewatering sludges.

annular space (AN-you-ler). A ring-shaped space located

between two circular objects, such as two pipes.

anode (an-0-d). The positive pole or electrode of an electro-

lytic system, such as a battery. The anode attracts nega-

tively charged particles or ions (anions).

antagonism. Interference or inhibition of the effect of one

chemical by the action of another chemical.

appropriative. Water rights to or ownership of a water

supply which is acquired for the beneficial use of water by

following a specific legal procedure.

appurtenance (uh-PURR-ten-nans). Machinery, appliances,

structures and other parts of the main structure necessary to

allow it to operate as intended, but not considered part of

the main structure.

aquatic. Plants of animal life living in, growing in, or

adapted to water.

aqueous (A-kwee-us). Something made up of, similar to, or

containing water; watery.

aquifer (ACK-wi-fer). A natural underground layer of

porous, water-bearing materials (sand, gravel) usually

capable of yielding a large amount or supply of water.

artesian (are-TEE-zhun - aquifer or well). Water held

under pressure in porous rock or soil confined by imperme-

able geologic formations. An artesian well is free flowing.

See confined aquifer


aseptic (a-SEP-tick). Free from the living germs of disease,

fermentation or putrefaction. Sterile.

assay. A test for a particular chemical or effect.

Association of Boards of Certification. An international

organization representing over 150 boards which certify the

operators of waterworks and waste water facilities. For

information on ABC publications regarding the preparation

of and how to study for operator certification examinations,

contact ABC, 4261/2 Fifth Street, P.O. Box 786, Ames,

Iowa 50010-0786.

asymmetric (A-see-MET-rick). Not similar in size, shape,

form or arrangement of parts on opposite sides of a line,

point or plane.

atom. The smallest unit of a chemical element; composed of

protons, neutrons and electrons.

available chlorine. A measure of the amount of chlorine

available in chlorinated lime, hypochlorite compounds, and

other materials that are used as a source of chlorine when

compared with that of elemental (liquid or gaseous)


available expansion. The vertical distance from the sand

surface to the underside of a trough in a sand filter. This

distance is also called FREEBOARD.

axial to impeller. The direction in which material being

pumped flows around the impeller or flow parallel to the

impeller shaft.

axis of impeller. An imaginary line running along the center

of a shaft (such as an impeller shaft).


back pressure. A pressure that can cause water to backflow

into the water supply when a user's water system is at a

higher pressure than the public water system.

backflow. A reverse flow condition, created by a difference

in water pressures, which causes water to flow back into the

distribution pipes of a potable water supply from any source

or sources other than an intended source. Also see backsi-

phonage and cross-connection.

background level. In toxic substances monitoring, the

average presence of a substance in the environment,

originally referring to naturally occurring phenomena.

backsiphonage. A form of backflow caused by a negative or

below atmospheric pressure within a water system. Also see

backflow and cross-connection.

backwashing. The process of reversing the flow of water

back through the filter media to remove the entrapped


bacteria (back-TEER-e-uh). Singular: bacterium. Micro-

scopic living organisms usually consisting of a single cell.

Bacteria can aid in pollution control by consuming or

breaking down organic matter in sewage, or by similarly

acting on oil spills or other water pollutants. Some bacteria

in soil, water or air may also cause human, animal and plant

health problems.

baffle. A flat board or plate, deflector, guide or similar device

constructed or placed in flowing water or slurry systems to

cause more uniform flow velocities, to absorb energy, and

to divert, guide, or agitate liquids (water, chemical solu-

tions, slurry).

bailer (BAY-ler). A 10- to 20-foot-long pipe equipped with a

valve at the lower end. A bailer is used to remove slurry

from the bottom or the side of a well as it is being drilled.

base metal. A metal (such as iron) which reacts with dilute

hydrochloric acid to form hydrogen. Also see noble metal.

batch process. A treatment process in which a tank or reactor

is filled, the water is treated or a chemical solution is

prepared, and the tank is emptied. The tank may then be

filled and the process repeated.

best available technology (BAT). The best technology

treatment techniques, or other means which the Administra-

tor finds, after examination for efficacy under field condi-

tions and not solely under laboratory conditions, are

available (taking cost into consideration). For the purposes

of setting MCLs for synthetic organic chemicals, any BAT

must be at least as effective as granular activated carbon.

best management practices (BMPs). Structural,

nonstructural and managerial techniques that are recognized

to be the most effective and practical means to control

nonpoint source pollutants yet are compatible with the

productive use of the resource to which they are applied.

BMPs are used in both urban and agricultural areas.

bias. An inadequacy in experimental design that leads to

results or conclusions not representative of the population

under study.

bioaccumulation. The retention and concentration of a

substance by an organism.

bioassay. Test which determines the effect of a chemical on a

living organism.

biochemical oxygen demand (BOD). The amount of oxygen

consumed by microorganisms (mainly bacteria) and by

chemical reactions in the biodegradation of organic matter.

bioconcentration. The accumulation of a chemical in tissues

of an organism (such as fish) to levels that are greater than

the level in the medium (such as water) in which the

organism resides (see bioaccumulation).

biodegradation. Decomposition of a substance into more

elementary compounds by the action of microorganisms

such as bacteria.

biological growth. The activity and growth of any and all

living organisms.

bioremediation. A process of adding nutrient to ground

water to speed up the natural process in which bacteria

break down gasoline into harmless compounds.

biotransformation. Conversion of a substance into other

compounds by organisms; includes biodegradation.

black water. Liquid and solid human body waste and the

carriage water generated through toilet usage.

blank. A bottle containing only dilution water or distilled

water; the sample being tested is not added. Tests are

frequently run on a SAMPLE and a BLANK and the

differences are compared.

BOD. See biochemical oxygen demand.

bonnet (BON-it). The cover on a gate valve.

brackish. Mixed fresh and salt waters.

brake horsepower. 1) The horsepower required at the top or

end of a pump shaft (input to a pump). 2) The energy

provided by a motor or other power source.

breakpoint chlorination. Addition of chlorine to water until

the chlorine demand has been satisfied. At this point,

further additions of chlorine will result in a free residual

chlorine that is directly proportional to the amount of

chlorine added beyond the breakpoint.

breakthrough. A crack or break in a filter bed allowing the

passage of floc or particulate matter through a filter. This

will cause an increase in filter effluent turbidity. A break-

through can occur: 1) when a filter is first placed in service,

2) when the effluent valve suddenly opens or closes, and 3)

during periods of excessive head loss through the filter

(including when the filter is exposed to negative heads).

brinelling (bruh-NEL-ing). Tiny indentations (dents) high

on the shoulder of the bearing race or bearing. A type of

bearing failure.

buffer. A solution or liquid whose chemical makeup neutral-

izes acids or bases without a great change in pH.

buffer capacity. A measure of the capacity of a solution or

liquid to neutralize acids or bases. This is a measure of the

capacity of water for offering a resistance to changes in pH.

buffer strips. Strips of grass or other close-growing vegeta-

tion that separate a waterway (ditch, stream, creek) from an

intensive land use area (subdivision, farm); also referred to

as filter strips, vegetated filter strips, and grassed buffers.

bw. Body weight.


C factor. A factor of value used to indicate the smoothness

of the interior of a pipe. The higher the C Factor, the smoother

the pipe, the greater the carrying capacity, and the smaller

the friction or energy losses from water flowing in the pipe.

To calculate the C Factor, measure the flow, pipe diameter,

distance between two pressure gages, and the friction or

energy loss of the water between the gages.

C Factor = Flow (GPM)/193.75 (Diameter, ft)2.63 (Slope)0.54

caisson (KAY-sawn). A structure or chamber which is

usually sunk or lowered by digging from the inside. Used to

gain access to the bottom of a stream or other body of


CAG. Carcinogen Assessment Group.

calcium carbonate (CACO3 ) equivalent. An expression of

the concentration of specified constituents in water in terms

of their equivalent value to calcium carbonate. For example,

the hardness in water which is caused by calcium, magne-

sium and other ions is usually described as calcium carbon-

ate equivalent.

calibration. A procedure which checks or adjusts an

instrument's accuracy by comparison with a standard or


cancer. A disease characterized by the rapid and uncontrolled

growth of aberrant cells into malignant tumors.

capillary action. The movement of water through very small

spaces due to molecular forces.

capillary forces. The molecular forces which cause the

movement of water through very small spaces.

capillary fringe. The porous material just above the water

table which may hold water by capillarity (a property of

surface tension that draws water upwards) in the smaller

void spaces.

capital costs. Costs (usually long-term debt) of financing

construction and equipment. Capital costs are usually fixed,

one-time expenses which are independent of the amount of

water produced.

carcinogen (car-SIN-o-jen). Any substance which tends to

produce cancer in an organism.

carcinogenic. Cancer-producing.

CAS registration number. A number assigned by the

Chemical Abstracts Service to identify a chemical.

catalyst (CAT-uh-LIST). A substance that changes the speed

or yield of a chemical reaction without being consumed or

chemically changed by the chemical reaction.

catalyze (CAT-uh-LIZE). To act as a catalyst. Or, to speed

up a chemical reaction.

catalyzed (CAT-uh-LIZED). To be acted upon by a catalyst.

cathode (KA-thow-d). The negative pole or electrode of an

electrolytic cell or system. The cathode attracts positively

charged particles or ions (cations).

cathodic protection (ca-THOD-ick). An electrical system

for prevention of rust, corrosion, and pitting of metal

surfaces which are in contact with water or soil. A low-

voltage current is made to flow through a liquid (water) or a

soil in contact with the metal in such a manner that the

external electromotive force renders the metal structure

cathodic. This concentrates corrosion on auxiliary anodic

parts which are deliberately allowed to corrode instead of

letting the structure corrode.

cation (CAT-EYE-en). A positively charged ion in an

electrolyte solution, attracted to the cathode under the

influence of a difference in electrical potential. Sodium ion

(Na+) is a cation.

cationic polymer. A polymer having positively charged

groups of ions; often used as a coagulant aid.

cavitation (CAV-uh-TAY-shun). The formation and

collapse of a gas pocket or bubble on the blade of an

impeller or the gate of a valve. The collapse of this gas

pocket or bubble drives water into the impeller or gate with

a terrific force that can cause pitting on the impeller or gate

surface. Cavitation is accompanied by loud noises that

sound like someone is pounding on the impeller or gate

with a hammer.

central nervous system. Portion of the nervous system

which consists of the brain and spinal cord; CNS.

centrate. The water leaving a centrifugal after most of the

solids have been removed.

centrifugal pump (sen-TRIF-h-gull). A pump consisting of

an impeller fixed on a rotating shaft that is enclosed in a

casing, and having an inlet and discharge connection. As the

rotating impeller whirls the water around, centrifugal force

builds up enough pressure to force the water through the

discharge outlet.

centrifuge. A mechanical device that uses centrifugal or

rotational forces to separate solids from liquids.

check valve. A special valve with a hinged disc or flap that

opens in the direction of normal flow and is forced shut

when flows attempt to go in the reverse or opposite direc-

tion of normal flow.

chelation (key-LAY-shun). A chemical complexing (form-

ing or joining together) of metallic cations (such as copper)

with certain organic compounds, such as EDTA (ethylene

diamine tetracetic acid). Chelation is used to prevent the

precipitation of metals (copper). Also see sequestration.

chemical oxygen demand (COD). An indirect measure of

the amount of oxygen used by inorganic and organic matter

in water. The measure is a laboratory test based on a

chemical oxidant and therefore does not necessarily

correlate with biochemical oxygen demand.

chisel plowing. Cropland preparation by a special implement

(chisel) that avoids complete inversion of the soil (as occurs

with conventional moldboard plowing). Chisel plowing can

leave a protective cover of crop residues on the soil surface

that helps prevent erosion and improve infiltration.

chloramines (KLOR-uh-means). Compounds formed by the

reaction of hypochlorous acid (or aqueous chlorine) with


chlorination (KLOR-uh-NAY-shun). The application of

chlorine to water, generally for the purpose of disinfection,

but frequently for accomplishing other biological or

chemical results (aiding coagulation and controlling tastes

and odors).

chlorinator (KLOR-uh-NAY-ter). A metering device which

is used to add chlorine to water.

chlorine-contact chamber. That part of a water treatment

plant where effluent is disinfected by chlorine.

chlorine demand. Chlorine demand is the difference

between the amount of chlorine added to water and the

amount of residual chlorine remaining after a given contact

time. Chlorine demand may change with dosage, time,

temperature, pH, and nature and amount of the impurities in

the water.

Chlorine Demand, mg/L = Chlorine Applied, mg/L - Residual, mg/L

chlorine requirement. The amount of chlorine which is

needed for a particular purpose. Some reasons for adding

chlorine are reducing the number of coliform bacteria (Most

Probable Number), obtaining a particular chlorine residual,

or oxidizing some substance in the water. In each case a

definite dosage of chlorine will be necessary. This dosage is

the chlorine requirement.

chlorophenolic (klor-o-FEE-NO-lick). Chlorophenolic

compounds are phenolic compounds (carbolic acid)

combined with chlorine.

chlorophenoxy (KLOR-o-fuh-KNOX-ee). A class of

herbicides that may be found in domestic water supplies

and cause adverse health effects. Two widely used

chlorophenoxy herbicides are 2,4-D (2,4-Dichlorophenoxy

acetic acid) and 2,4,5-TP (2,4,5-Trichlorophenoxy propi-

onic acid (silvex)).

chlororganic (klor-or-GAN-nick). Organic compounds

combined with chlorine. These compounds generally

originate from, or are associated with, life processes such as

those of algae in water.

chronic. Occurring over a long period of time, either continu-

ously or intermittently; used to describe ongoing exposures

and effects that develop only after a long exposure.

chronic exposure. Long-term, low-level exposure to a toxic


circle of influence. The circular outer edge of a depression

produced in the water table by the pumping of water from a

well. Also see cone of influence and cone of depression.

circuit. The complete path of an electric current, including

the generating apparatus or other source; or, a specific

segment or section of the complete path.

circuit breaker. A safety device in an electrical circuit that

automatically shuts off the circuit when it becomes over-

loaded. The device can be manually reset.

cistern (SIS-turn). A small tank (usually covered) or a

storage facility used to store water for a home or farm.

Often used to store rain water.

clarifer (KLAIR-uh-fire). A large circular or rectangular

tank or basin in which water is held for a period of time,

during which the heavier suspended solids settle to the

bottom. Clarifiers are also called SETTLING BASINS and


class (pipe and fittings). The working pressure rating of a

specific pipe for use in water distribution systems which i

includes allowances for surges. This term is used for cast

iron, ductile iron, asbestos cement and some plastic pipe.

clay. One type of soil particle with a diameter of approxi-

mately one ten-thousandth of an inch.

clay soil. A soil containing more than 40 percent clay, but

less than 45 percent sand, and less than 40 percent silt.

clear well. A reservoir for the storage of filtered water of

sufficient capacity to prevent the need to vary the filtration

rate with variations in demand. Also used to provide

chlorine contact time for disinfection.

clinical studies. Studies of humans suffering from symptoms

induced by chemical exposure.

coagulant aid. Any chemical or substance used to assist or

modify coagulation.

coagulants (co-AGG-you-lents). Chemicals that cause very

fine particles to clump together into larger particles. This

makes it easier to separate the solids from the water by

settling, skimming, draining or filtering.

coagulation (co-AGG-yoo-LAY-shun). The clumping

together of very fine particles into larger particles caused by

the use of chemicals (coagulants). The chemicals neutralize

the electrical charges of the fine particles and cause

destabilization of the particles. This clumping together

makes it easier to separate the solids from the water by

settling, skimming, draining, or filtering.

cohesion. Molecular attraction which holds two particles


coliform (COAL-i-form). A group of bacteria found in the

intestines of warm-blooded animals (including humans)

also in plants, soil, air and water. Fecal coliforms are a

specific class of bacteria which only inhibit the intestines of

warm-blooded animals. The presence of coliform a is

an indication that the water is polluted and may contain

pathogenic organisms.

coliform organism. Microorganisms found in the intestinal

tract of humans and animals. Their presence in water

indicates fecal pollution and potentially dangerous bacterial

contamination by disease-causing microorganisms.

colloids (CALL-loids). Very small, finely divided solids

(particles that do not dissolve) that remain dispersed in a

liquid for a long time due to their small size and electrical

charge. When most of the particles in water have a negative

electrical charge, they tend to repel each other. This

repulsion prevents the particles from clumping together,

becoming heavier, and settling out.

colorimetric measurement. A means of measuring unknown

chemical concentrations in water by measuring a sample's

color intensity. The specific color of the sample, developed

by addition of chemical reagents, is measured with a

photoelectric colorimeter or is compared with "color

standards" using, or corresponding with, known concentra-

tions of the chemical.

combined available residual chlorine. The concentration of

residual chlorine which is combined with ammonia (NH3)

and/or organic nitrogen in water as a chloramine (or other

chloro derivative) yet is still available to oxidize organic

matter and utilize its bactericidal properties.

combined residual chlorination. The application of chlorine

to water to produce combined available residual chlorine.

This residual can be made up of monochloramines,

dichloramines, and nitrogen trichloride.

combined sewer. A sewer that transports surface runoff and

human domestic wastes (sewage), and sometimes industrial

wastes. Wastewater and runoff in a combined sewer may

occur in excess of the sewer capacity and cannot be treated

immediately. The excess is frequently discharged directly

to a receiving stream without treatment, or to a holding

basin for subsequent treatment and disposal.

community water system (C.W.S.). A public water system

which serves at least 15 service connections used by year-

round residents or regularly serves at least 25 year-round

residents. Also see non-community water system, transient

water system and non-transient non-community water


complete treatment. A method of treating water which

consists of the addition of coagulant chemicals, flash

mixing, coagulation - flocculation, sedimentation and

filtration. Also called CONVENTIONAL FILTRATION.

compliance cycle. Thee nine-year calendar year cycle during

which public water systems must monitor. Each compliance

cycle consists of three three-year compliance periods. The

first calendar year cycle begins January 1, 1993 and ends

December 31, 2001; the second begins January 1, 2002 and

ends December 31, 2010; the third from January 1, 2011 to

December 31, 2019, etc.

compliance period. A three year calendar period within a

compliance cycle. Each compliance cycle has three three-

year compliance periods. Within the first compliance cycle,

the first compliance period runs from January 1, 1993 to

December 31, 1995; the second from January 1, 1996 to

December 31, 1998; the third from January 1, 1999 to

December 31, 2001.

composite (proportional) samples (come-PAH-zit). A

composite sample is a collection of individual samples

obtained at regular intervals, usually every one or two hours

during a 24-hour time span. Each individual sample is

combined with the others in proportion to the rate of flow

when the sample was collected The resulting mixture

(composite sample) forms a representative sample and is

analyzed to determine the average conditions during the

sampling period.

composting. A controlled microbial degradation of organic

waste yield an environmentally sound, nuisance-free

product of potential value as a soil conditioner.

compound. A substance composed of two or more elements

whose composition is constant. For example, table salt

(sodium chloride - NACl) is a compound.

concentration polarization. 1) The ratio of the salt concen-

tration in the membrane boundary layer to the salt concen-

tration in the bulk stream. The most common and serious

problem resulting from concentration polarization is the

increasing tendency for precipitation of sparingly soluble

salts and the deposition of particulate matter on the mem-

brane surface. 2) Used in corrosion studies to indicate a

depletion of ions near an electrode. 3) The basis for

chemical analysis by a polarograph.

conductance. A rapid method of estimating the dissolved-

solids content of a water supply. The measurement indicates

the capacity of a sample of water to carry an electrical

current, which is related to the concentration of ionized

substances in the water. Also called SPECIFIC CONDUC-


conductivity. A measure of the ability of a solution (water) to

carry an electric current.

conductor. A substance, body, device or wire that readily

conducts or carries electrical current.

cone of depression. The depression, roughly conical in

shape, produced in the water table by the pumping of water

from a well. Also see circle of influence and cone of


cone of influence. The depression, roughly conical in shape,

produced in the water table by the pumping of water from a

well. Also see circle of influence and cone of depression

confined aquifer. An aquifer in which ground water is

confined under pressure which is significantly greater than

atmospheric pressure. See artesian aquifer.

confluent growth. A continuous bacterial growth covering

the entire filtration area of a membrane filter, or a portion

thereof, in which bacterial colonies are not discrete.

confounding factors. Variables other than chemical exposure

level which can affect the incidence or degree of a para-

meter being measured.

consumptive use. Water removed from available supplies

without direct return to a water resource system for uses

such as manufacturing, agriculture, and food preparation.

contactor. An electrical switch, usually magnetically


contaminant Any physical, chemical, biological, or radio-

logical substance or matter that has an adverse effect on air,

water, or soil.

contamination. The introduction into water of microorgan-

isms, chemicals, toxic substances, wastes, or wastewater in

a concentration that makes the water unfit for its next

intended use.

continuous sample. A flow of water from a particular place

in a plant to the location where samples are collected for

testing. This continuous stream may be used to obtain grab

or composite samples. Frequently, several taps (faucets)

will flow continuously in the laboratory to provide test

samples from various places in a water treatment plant.

contour farming. A conservation-based method of farming

in which all farming operations (for example, tillage and

planting) are performed across (rather than up and down)

the slope. Ideally, each crop row is planted at right angles

to the ground slope.

contour strip farming. A kind of contour farming in which

row crops are planted in strips, between alternating strips of

close-growing, erosion resistant forage (grass, grain, hay)


control loop. The path through the control system between

the sensor, which measures a process variable, and the

controller, which controls or adjusts the process variable.

control system. A system which senses and controls its own

operation on a close, continuous basis in what is called

proportional (or modulating) control.

controller. A device which controls the starting, stopping, or

operation of a device or piece of equipment.

conventional filtration. A method of treating water to

remove particulates. The method consists of the addition of

coagulant chemicals, flash mixing, coagulation - floccula-

tion, sedimentation and filtration. Also called COMPLETE

TREATMENT. Also see direct filtration and in-line


conventional filtration treatment A series of processes

including coagulation, flocculation, sedimentation, and

filtration resulting in substantial particulate removal.

conventional tillage. The traditional method of farming in

which soil is prepared for planting by completely inverting

it with a moldboard plow. Subsequent working of the soil

with other implements is usually performed to smooth the

soil surface. Bare soil is exposed to the weather for some

varying length of time depending on soil and climatic


conventional treatment See conventional filtration Also


conveyance loss. Water lost in conveyance (pipe, channel,

conduit, ditch) by leakage or evaporation.

corporation stop. A water service shutoff valve located at a

street water main. This valve cannot be operated from the

ground surface because it is buried and there is no valve

box. Also called a CORPORATION COCK.

corrosion. The gradual decomposition or destruction of a

material by chemical action, often due to an electrochemi-

cal reaction. Corrosion may be caused by: 1) stray current

electrolysis, 2) galvanic corrosion caused by dissimilar

metals, or 3) differential concentration cells. Corrosion

starts at the surface of a material and moves inward.

corrosion inhibitor. A substances that slows the rate of

corrosion of metal plumbing materials by water, especially

lead and copper materials, by forming a protective film on

the interior surface of those materials.

corrosivity. An indication of the corrosiveness of a water.

The corrosiveness of a water is described by the water's pH,

alkalinity, hardness, temperature, total dissolved solids,

dissolved oxygen concentration, and the Langelier Index.

cost/beneflt analysis. A quantitative evaluation of the costs

which would be incurred versus the overall benefits to

society of a proposed action such as the establishment of an

acceptable dose of a toxic chemical.

cost sharing. A publicly financed program through which

society, as the beneficiary of environment protection, shares

part of the cost of pollution control with those who must

actually install the controls.

coulomb (COO-lahm). A measurement of the amount of

electrical charge conveyed in one second by an electric

current of one ampere. One coulomb equals about 6.25 x

1018electrons (6,250,000,000,000,000,000 electrons).

coupon. A steel specimen inserted into water to measure the

corrosiveness of water. The rate of corrosion is measured as

the loss of weight of the coupon (in milligrams) per surface

area (in square decimeters) exposed to the water per day. 10

decimeters = 1 meter = 100 centimeters

cover crop. A crop that provides temporary protection for

delicate seedlings and/or provides a canopy for seasonal soil

protection and improvement between normal crop produc-

tion periods. Except in orchards where permanent vegeta-

tive cover is maintained, cover crops usually are grown for

one year of less. When plowed under and incorporated into

the soil, cover crops are also referred to as gren manure


crop rotation. A system of farming in which a regular

succession of different crops are planted on the same land

area, as opposed to growing the same crop time after time


cross connection. Any actual or potential connection

between a drinking (potable) water system and an

unapproved water supply or other source of contamination.

For example, if you have a pump moving nonpotable water

and hook into the g water system to supply water for

the pump seal, a cross-connection or mixing between the

two water systems can occur. This mixing may lead to

contamination of the drinking water. Also see backsiphon-

age and backflow.

CT or CTcalc. The product of "residual disinfectant concen-

tration" (C) in mg/l determined before or at the first

customer, and the corresponding "disinfectant contact time"

(T) in minutes, i.e., "C" x "T". If a public water system

applies disinfectants at more than one point prior to the first

customer, it must determine the CT of each disinfectant

sequence before or at the first customer to determine the

total percent inactivation or "total inactivation ratio".In

determining the total inactivation ratio, the public water

system must determine the residual disinfectant concentra-

tion of each disinfection sequence and corresponding

contact time before any subsequent disinfection application

point(s). "CT99.9" is the CT value required for 99.9 Percent

(3-log) inactivation of Giardia lamblia cysts. CT99.9 a variety

of disinfectants and conditions appear in Tables 1. l- 1.6, 2.1,

and 3.1 of section 141.74(b)(3) in the code of Federal


CT99.9 is the inactivation ratio. The sum of the inactivation

ratios, or total inactivation ratio shown as

E = (CT calc) / (CT99.9)

is calculated by adding together the inactivation ratio

for each disinfection sequence. A total inactivation ratio

equal to or greater than 1.0 is assumed to provide a 3-log

inactivation of Giardia lamblia cysts.

cumulative exposure. The summation of exposures of an

organism to a chemical over a period of time.

curb stop. A water service shutoff valve located in a water

service pipe near the curb and between the water main and

the building. This valve is usually operated by a wrench or

valve key and is used to start or stop flows in the water

service line to a building. Also called a "curb cock."

curie. A measure of radioactivity. One Curie of radioactivity

is equivalent to 3.7 x 1010 or 37,000,000,000 nuclear

disintegrations per second.

current. A movement or flow of electricity. Water flowing in

a pipe is measured in gallons per second past a certain

point, not by the number of water molecules going past a

point. Electric current is measured by the number of

coulombs per second flowing past a certain point in a

conductor. A coulomb is equal to about 6.25 x 1018 elec-

trons (6,250,000,000,000,000,000 electrons). A flow of one

coulomb per second is called one ampere, the unit of the

rate of flow of current.


dateometer (day-TOM-uh-ter). A small calendar disc

attached to motors and equipment to indicate the year in

which the last maintenance service was performed.

day tank. A tank used to store a chemical solution of known

concentration for feed to a chemical feeder. A day tank

usually stores sufficient chemical solution to properly treat

the water being treated for at least one day. Also called an


dead end. The end of a water main which is not connected to

other parts of the distribution system by means of a con-

necting loop of pipe

decant To draw off the upper layer of liquid (water) after the

heavier material (a solid or another liquid) has settled.

dechlorination (dee-KLOR-uh-NAY-shun). The deliberate

removal of chlorine from water. The partial or complete

reduction of residual chlorine by any chemical or physical


decibel (DES-uh-bull). A unit for expressing the relative

intensity of sounds on a scale from zero for the average

least perceptible sound to about 130 for the average level at

which sound causes pain to humans.

decomposition. The conversion of chemically unstable

materials to more stable forms by chemical or biological

action. If organic matter decays when there is no oxygen

present (anaerobic conditions or putrefaction), undesirable

tastes and odors are produced. Decay of organic matter

when oxygen is present (aerobic conditions) tends to

produce much less objectionable tastes and odors.

defluoridation (de-FLOOR-uh-DAY-shun). The removal

of excess fluoride in drinking water to prevent the mottling

(brown stains) of teeth.

degasification (DEE-GAS-if-uh-KAY-shun). A water

treatment process which removes dissolved gases from the

water. The gases may be removed by either mechanical or

chemical treatment methods or a combination of both.

degradation. Chemical or biological breakdown of a

complex compound into simpler compounds.

demineralization (DEE-MIN-er-al-uh-ZAY-shun). A

treatment process which removes dissolved minerals (salts)

from water.

denitrification. The biochemical conversion of nitrate; and

nitrite nitrogen in the soil dissolved in water to gaseous


density (DEN-sit-tee). A measure of how heavy a substance

(solid, liquid or gas) is for its size. Density is expressed in

terms of weight per unit volume, that is, grams per cubic

centimeter or pounds per cubic foot. The density of water is

1.0 gram per cubic centimeter or about 62.4 pounds per

cubic foot.

dermal exposure. Contact between a chemical and the skin.

desalinization (DEE-SAY-leen-uh-ZAY-shun). The

removal of dissolved salts (such as sodium chloride, NACI)

from water by natural means (leaching) or by specific water

treatment processes.

desiccant (DESS-uh-kant). A drying agent which is capable

of removing or absorbing moisture from the atmosphere in

a small enclosure.

desiccation (DESS-uh-KAY-shun). A process used to

thoroughly dry air; to remove virtually all moisture from


desiccator (DESS-uh-KAY-tor). A closed container into

which heated weighing or drying dishes are placed to coot

in a dry environment. The dishes may be empty or they may

contain a sample. Desiccators contain a substance, such as

anhydrous calcium chloride, which absorbs moisture and

keeps the relative humidity near zero so that the dish or

sample will not gain weight from absorbed moisture.

destratification (de-STRAT-uh-fuh-KAY-shun).The

development of vertical mixing within a lake or reservoir to

eliminate (either totally or partially) separate layers of

temperature, plant, or animal life. This vertical mixing can

be caused by mechanical means (pumps) or through the use

of forced air diffusers which release air into the lower

layers of the reservoir.

detention lag. The time period between the moment a change

is made and the moment when such a change is finally

sensed by the associated measuring instrument.

detention time. 1) The theoretical (calculated) time required

for a small amount of water to pass through a tank at a

given rate of flow. 2) The actual time in hours, minutes or

seconds that a small amount of water is in a settling basin,

flocculating basin or rapid-mix chamber. In storage

reservoirs, detention time is the length of time entering

water will be held before being drafted for use (several

weeks to years, several months being typical).

Detention Time (hr) =

Basin Volume (gal.)(24 hr/day)t Flow (gal/day)

dew point. The temperature to which air with a given

quantity of water vapor must be cooled to cause condensa-

tion of the vapor in the air.

dewater. 1) To remove or separate a portion of the water

present in a sludge or slurry. To dry sludge so it can be

handled and disposed. 2) To remove or drain the water from

a tank or a trench.

diatomaceous earth. A fine, siliceous (made of silica)

"earth" composed mainly of the skeletal remains of dia-

toms, a type of free-floating, microscopic plant found in the


diatomaceous earth filtration (DE filtration). A filtration

method resulting in substantial particulate removal, that

uses a process in which: 1) a "precoat" cake of diatoma-

ceous earth filter media is deposited on a support membrane

(septum), and 2) while the water is filtered by passing

through the cake on the septum, additional filter media,

known as "body feed," is continuously added to the feed

water to maintain the permeability of the filter cake.

diffusion. The movement of suspended or dissolved particles

from a more concentrated to a less concentrated region as a

result of the random movement of individual particles; the

process tends to distribute them uniformly throughout the

available volume.

digital readout Use of numbers to indicate the value or

measurement of a variable. The readout of an instrument by

a direct, numerical reading of the measured value.

dilute solution. A solution that has been made weaker

usually by the addition of water.

dimictic (die-MICK-tick). Lakes and reservoirs which freeze

over and normally go through two stratification and two

mixing cycles within a year.

direct current (D.C.). Electrical current flowing in one

direction only and essentially free from pulsation.

direct filtration. A filtration method of treating water which

consists of the addition of coagulant chemicals, flash

mixing, coagulation, minimal flocculation, and filtration.

The flocculation facilities may be omitted, but the physical-

chemical reactions will occur to some extent. The sedimen-

tation process is omitted. Also see conventional filtration

and in-line filtration.

direct runoff. Water that flows over the ground surface or

through the ground directly into streams, rivers, or lakes.

discharge head. The pressure (in pounds per square inch or

psi) measured at the centerline of a pump discharge and

very close to the discharge flange, converted into feet.

disinfectant. Any oxidant, including but not limited to

chlorine, chlorine dioxide, chloramines, and ozone, that is

added to water in any part of the treatment or distribution

process and is intended to kill or inactivate pathogenic


disinfectant contact time ("T" in CT calculations). The

time in minutes that it takes for water to move from the

point of disinfectant application or the previous point of

disinfectant residual measurement to a point before or at the

point where residual disinfectant concentration (C) Is

measured. Where only one C is measured. T is the time in

minutes that it takes for water to move from the point of

disinfectant application to a point before or at where

residual disinfectant concentration (C) is measured. Where

more than one C is measured, T is (a) for the first measure-

ment of C, the time in minutes that it takes for water to

move from the first or only point of disinfectant application

to a point before or at the point where the first C+ is

measured and (b) for subsequent measurements of C, the

time in minutes that it takes for water to move from the

previous C measurement point to the C measurement point

for which the particular T is being calculated- Disinfectant

contact time in pipelines must be calculated based on plug

flow by dividing the internal volume of the pipe by the

maximum hourly flow rate through that pipe. Disinfectant

contact time within mixing basins and storage reservoirs

must be determined by tracer studies or an equivalent


disinfection. The process designed to kill most microorgan-

isms in water, including essentially all pathogenic (disease-

causing) bacteria. There are several ways to disinfect, with

chlorine being most frequently used in water treatment.

Compare with sterilization.

disinfection by-product A compound formed by the

reaction of a disinfectant such as chlorine with organic

material in the water supply.

dissolved oxygen (DO). Measure of water quality indicating

free oxygen dissolved in water.

distillate (DIS-tuh-late). In the distillation of a sample, a

portion is evaporated; the part that is condensed afterwards

is the distillate.

divalent (die-VAY-lent). Having a valence of two, such as

the ferrous ion, Fe2+.

diversion. 1) Use of part of a stream flow as a water

supply. 2) A structural conveyance (or ditch) constructed

across a slope to intercept runoff flowing down a hillside,

and divert it to some convenient discharge point.

Domestic or Other Non-distribution System Plumbing

Problem. A coliform contamination problem in a public

water system with more than one service connection that is

limited to the specific service connection from which the

coliform positive sample was taken.

dosage. The quantity of a chemical administered to an


dose. The actual quantity of a chemical to which an organism

is exposed. See absorbed dose.

dose equivalent. The product of the absorbed dose from

ionizing radiation and such factors as account for differ-

ences In biological effectiveness due to the " of radiation

and is distribution in the body as specified by the Interna-

tional Commission on Radiological Units and Measure-

ments (ICRU).

dose-response. A quantitative relationship between the dose

of a chemical and an effect caused by the chemical.

dose-response curve. A graphical presentation of the

relationship between degree of exposure to a chemical

(dose) and observed biological effect or response.


dose-response evaluation. A component of risk assessment

that describes the quantitative relationship between the

amount of exposure to a substance and the extent of toxic

injury or disease.

dose-response relationship. The quantitative relationship

between the amount of exposure to a substance and the

extent of toxic injury produced.

downgradients The direction that ground water flows;

similar in concept to: downstream for surface water, such

as a river.

DPD (pronounce as separate letters). A method of measur-

ing the chlorine residual in water. The residual may be

determined by either titrating or comparing a developed

color with color standards. DPD stands for N,N-diethyl-p-


draft 1) The act of drawing or removing water from a tank

or reservoir. 2) The water which is drawn or removed from

a tank or reservoir.

drainage. A technique to improve the productivity of some

agricultural land by removing excess water from the soil;

surface drainage is accomplished with open ditches;

subsurface drainage uses porous conduits (drain tile) buried

beneath the soil surface.

drainage basin. The area of land that drains water, sediment,

and dissolved materials to a common outlet at some point

along a stream channel. Also see watershed.

drawdown. 1) The drop in the water table or level of water in

the ground when water is being pumped from a well. 2) The

amount of water used from a tank or reservoir. 3) The drop

in the water level of a tank or reservoir.

DWEL (Drinking Water Equivalent Level). Estimated

exposure (in mg/L) which is interpreted to be protective for

non carcinogenic endpoints of toxicity over a lifetime of

exposure. DWEL was developed for chemicals that have a

significant carcinogenic potential (Group B). Provides risk

manager with evaluation on non-cancer endpoints, but

infers that carcinogenicity should be considered the toxic

effect of greatest concern.

dynamic pressure. When a pump is operating, the vertical

distance (in feet) from a reference point (such as a pump

centerline) to the hydraulic grade line is the dynamic head.


eductor (e-DUCK-ter). A hydraulic device used to create a

negative pressure (suction) by forcing a liquid through a

restriction, such as a Venturi. An eductor or aspirator (the

hydraulic device) may be used in the laboratory in place of

a vacuum pump. As an injector, it is used to produce

vacuum for chlorinators.

effective corrosion Inhibitor residual. A concentration of

corrosion inhibitor sufficient to form a protective coating on

the interior walls of a pipe, reducing its corrosion.

effective range. That portion of the design range (usually

upper 90 percent) in which an instrument has acceptable

accuracy. Also see range and span

effective size (E.S.). The diameter of the particles in a

granular sample (filter media) for which 10 percent of the

total grains are smaller and 90 percent larger on a weight

basis. Effective size is obtained by passing granular

material through sieves with varying dimensions of mesh

and weighing the material retained by each sieve. The

effective size is also approximately the average size of the


effluent (EF-loo-ent). Water or some other liquid-raw,

partially or completely treated-flowing from a reservoir,

basin, treatment process or treatment plant.

ejector. A device used to disperse a chemical solution into

water being treated.

electrochemical reaction. Chemical changes produced by

electricity (electrolysis) or the production of electricity by

chemical changes (galvanic action). In corrosion, a chemi-

cal re-action is accompanied by the flow of electrons

through a metallic path. The electron flow may come from.

an external force and cause the reaction, such as electrolysis

caused by a D.C. (direct current) electric railway or the

electron flow may be caused by a chemical reaction as in

the galvanic action of a flashlight dry cell.

electrochemical sries. A list of metals with the standard

electrode potentials given in volts. The size and sip of the

electrode potential indicates how easily these elements will

take on or give up electrons, or corrode. Hydrogen is

conventionally assigned a value of zero.

electrolysis (ee-leck-TRAWL-us-sis). The decomposition of

material by an outside electrical current.

electrolyte (ee.-LECK-tro-LIGHT). A substance which

dissociates (separates) into two or more ions when it is

dissolved in water.

electrolytic cell (ee-LECK-tro-LIT-ick). A device in which

the chemical decomposition of material causes an electric

current to flow. Also, a device in which a chemical reaction

occurs as a result of the flow of electric current. Chlorine

and caustic (NaOH) are made from salt (NACl in electro-

lytic cells.

electromotive force (E.M.F.). The electrical pressure

available to cause a flow of current (amperage) when an

electrical circuit is closed. See voltage

electromotive series. A list of metals and alloys presented in

the order of their tendency to con-ode (or go into solution).

Also called the Galvanic Series. This is a practical applica-

tion of the theoretical ELECTROCHEMICAL SERIES.

electron. An extremely small, negatively charged particle;

the part of an atom that determines its chemical properties.

element. A substance which cannot be separated into its

constituent parts and still retain its chemical identity. For

example, sodium (Na) is an element.

end bells. Devices used to hold the rotor and stator of a motor

in position.

end point. Samples are titrated to the end point. This means

that a chemical is added, drop by drop, to a sample until a

certain color change (blue to clear, for example) occurs.

This is called the END POINT of the titration. In addition

to a color change, an end point may be reached by the

formation of a precipitate or the reaching of a specified pH.

An end point may be detected by the use of an electronic

device such as a pH meter.

endangerment assessment. A site-specific risk assessment

of the actual or potential danger to human health or welfare

and the environment from the release of hazardous sub-

stances or waste. The endangerment assessment document

is prepared in support of enforcement actions under


endemic (en-DEM-ick). Something peculiar to a particular

people or locality, such as a disease which is always present

in the population.

endrin (EN-drin). A pesticide toxic to freshwater and marine

aquatic life that produces adverse health effects in domestic

water supplies.

energy grade line (E.G.L.). A line that represents the

elevation of energy head of water flowing in a pipe, conduit

or channel. The line is drawn above the hydraulic grade line

(gradient) a distance equal to the velocity head (V2/2g) of

the water flowing at each section or point along the pipe or

channel. Also see hydraulic gradeline.

enteric. Of intestinal origin, especially applied to wastes or


entrain. To trap bubbles in water either mechanically through

turbulence or chemically through a reaction.

enzymes (EN-zimes). Organic substances (produced by

living organisms) which cause or speed up chemical

reactions. Organic catalysts and/or biochemical catalysts.

E-P.A. United States Environmental Protection Agency.

epidemic. Widespread outbreak of a disease, or a large

number of cases of a disease in a single community or

relatively small area. Disease may spread from person to

person, and/or by the exposure of many persons to a single

source, such as a water supply.

epidemiologic study. Study of human populations to identify

causes of disease. Such studies often compare the health

status of a group of persons who have been exposed to a

suspect agent with that of a comparable non-exposed group.

epidemiology (EP-uh-DE-me-ALL-o-gee). A branch of

medicine which studies epidemics (diseases which affect

significant numbers of people during the same time period

in the same locality). The objective of epidemiology is to

determine the factors that cause epidemic diseases and how

to prevent them.

epilimnion (EP-ub-LIM-knee-on). The upper layer of water

in a thermally stratified lake or reservoir. This layer consists

of the warmest water and has a fairly uniform (constant)

temperature. The layer is readily mixed by wind action.

erosion. Wearing away of soil by timing water, wind, or

ice; erosion is the process by which the earth's surface is

shaped and occurs even in remote, uninhabited areas at a

slow rate (geologic erosion); of more concern is accelerated

erosion caused by people's activities.

ester. A compound formed by the reaction between an acid

and an alcohol with the elimination of a molecule of water.

eutrophic (you-TRO-fick). Reservoirs and lakes which are

rich in nutrients and very productive in terms of aquatic

animal and plant life.

eutrophication (you-TRO-fi-KAY-shun). The increase in

the nutrient levels of a lake or other body of water; this

usually causes an increase in the growth of aquatic animal

and plant life.

evaporation. The process by which water or other liquid

becomes a gas (water vapor or ammonia vapor). Water

from land areas, bodies of water, and all other moist

surfaces is absorbed into the atmosphere as a vapor.

evapotranspiration (ee-VAP-o-TRANS-purr-A-shun). The

combined processes of evaporation and transpiration. It can

be defined as the sum of water used by vegetation and water

lost by evaporation.

exemption. A State with primacy may relieve a public water

system from a requirement respecting an MCL,treatment

technique or both, by granting an exemption if certain

conditions exist. These are: 1) the system cannot comply

with a MCL or treatment technique due to compelling

factors which may include economic factors; 2) the system

was in operation on the effective date of the MCL or

treatment technique requirement; and 3) the exemption will

not result in an unreasonable public health risk. Also see


exposure. Contact with a chemical or physical agent.

exposure assessment. The determination or estimation

(qualitative or quantitative) of the magnitude, frequency,

duration, route, and extent (number of people) of exposure

to a chemical.

exposure coefficient. Term which combines information on

the frequency, mode, and magnitude of contact with

contaminated medium to yield a quantitative value of the

amount of contaminated medium contacted per day.

exposure level (chemical). The amount (concentration) of a

chemical at the absorptive surfaces of an organism.

exposure scenario. A set of conditions or assumptions about

sources, exposure pathways, concentrations of toxic

chemicals and populations (numbers, characteristics and

habits) which aid the investigator in evaluating and quanti-

fying exposure in a given situation.

extrapolation. Estimation of unknown values by extending or

projecting from known values.


facultative (FACK-ul-TAY-tive). Facultative bacteria can

use either molecular (dissolved) oxygen or oxygen obtained

from food material such as sulfate or nitrate ions. In other

words, facultative bacteria can live under aerobic or

anaerobic conditions.

fecal coliform bacteria. Bacteria found in the intestinal tracts

of animals. Their presence in water or sludge is an

indicator of pollution and possible contamination by


feedback The circulating action between a sensor measuring

a process variable and the controller which controls or

adjusts the process variable .

filtration. A process for removing particulate matter from

water by passage through porous media.

finished water. Water that has passed through a water

treatment plant; all the treatment processes are completed or

"finished". This water is ready to be delivered to consum-

ers. Also called PRODUCT WATER.

first draw. The water that immediately comes out when a tap

is first opened. This water is likely to have the highest level

of lead contamination from plumbing materials.

first draw sample. A one-liter sample of tap water, collected

in accordance with CFR Section 141.86(b)(2), that has been

standing in plumbing pipes at least 6 hours and is collected

without flushing the tap.

fix, sample. A sample is fixed in the field by adding chemi-

cals that prevent the water quality indicators of interest in

the sample from changing before final measurements are

performed later in the lab.

flagellates (FLAJ-el-LATES). Microorganisms that move

by the action of tail-like projections.

flame polished. Melted by a flame to smooth out irregulari-

ties. Sharp or broken edges of glass (such as the end of a

glass tube) are rotated in aflame until the edge melts slightly

and becomes smooth.

floc. Clumps of bacteria and particulate impurities that have

come together and formed a cluster. Found in flocculation

tanks and settling or sedimentation basins.

flocculation. The gathering together of fine particles in water

by gentle mixing after the addition of coagulant chemicals

to form larger particles.

floodplain. The flat or nearly flat land on the floor of a

steam valley or tidal area that is covered by water during


fluidized (FLEW-id-i-zd). A mass of solid particles that is

made to flow like a liquid by injection of water or gas is

said to have been fluidized. In water treatment, a bed of

filter media is fluidized by backwashing water through the


fluoridation (FLOOR-uh-DAY-shun).The addition of a

chemical to increase the concentration of fluoride ions in

drinking water to a predetermined optimum limit to reduce

the incidence (number) of dental caries (tooth decay) in

children. Defluoridation is the removal of excess fluoride in

drinking water to prevent the mottling (brown stains) of


fluorosis. An abnormal condition caused by excessive intake

of fluorine, characterized chiefly by mottling of the teeth.

flush. I)To open a cold-water tap to clear out all the water

which may have been sitting for a long time in the pipes. m

new homes, to flush a system means to send large volumes

of water gushing through the unused pipes to remove loose

particles of solder and flux. 2) To force large amounts of

water through liquid to clean out piping or tubing. storage

or process tanks.

flushing. A method used to clean water distribution lines.

Hydrants are opened and water with a high velocity flows

through the pipes, removes deposits from the pipes, and

flows out the hydrants.

flux. A flowing or flow.

foot valve. A special type of check valve located at the

bottom end of the suction pipe on a pump. This valve opens

when the pump operates to allow water to enter the suction

pipe but closes when the pump shuts off to prevent water

from flowing out of the suction pipe.

formation. A group of similar consolidation (that is, rela-

tively solid) rocks of unconsolidated (that is, relatively

loose) minerals.

free available residual chlorine. That portion of the total

available residual chlorine composed of dissolved chlorine

gas cl2), hypochlorous acid (HOCl), and/or hypochlorite

ion (OCl-) remaining in water after chlorination. This does

not include chlorine that has combined with ammonia,

nitrogen, or other compounds.

free residual chlorination. The application of chlorine to

water to produce a free available chlorine residual equal to

at least 80 percent of the total residual chlorine (sum of free

and combined available chlorine residual).

freeboard. 1) The vertical distance from the normal water

surface to the top of the confining wall. 2) The vertical

distance from the sand surface to the underside of a trough

in a sand filter. This distance is also called AVAILABLE


friction losses. The head, pressure or energy (they are the

same) lost by water flowing in a pipe or channel as a result

of turbulence caused by the velocity of the flowing water

and the roughness of the pipe. channel walls, and restric-

tions caused by fittings. Water flowing in a pipe loses

pressure or energy as a result of friction losses. Also see

head loss.

fresh water. Water that generally contains less than 1,000

milligrams-per-liter of dissolved solids

fungi (FUN-ji). Mushrooms, molds, mildews, rusts, and

smuts that are small non-chlorophyll-bearing plants lacking

roots, stems and leaves. They occur in natural waters and

grow best in the absence of light. Their decomposition may

cause objectionable tastes and odors in water.


gage pressure. The pressure within a closed container or pipe

as measured with a gage. In contrast, absolute pressure is

the sum of atmospheric pressure (14.7 lbs/sq in) PLUS

pressure within a vessel (as measured by a gage). Most

pressure gages read in gage pressure or psig (pounds per

square inch gage pressure).

galvnic call. An electrolytic cell capable of producing

electrical energy by electrochemical action. The decomposi-

tion of materials in the cell causes an electric (electron)

current to flow from cathode to anode.

galvanic series. A list of metals and alloys presented in the

order of their tendency to corrode (or go into solution). Also

called the ELECTROMOTIVE SERIES. This is a practical

application of the theoretical ELECTROCHEMICAL


galvanize. To coat a metal (especially iron or steel) with zinc.

Galvanization is the process of coating a metal with zinc.

garnet (GAR-nit). A group of hard, reddish, glassy, mineral

sands made up of silicates of base metals (calcium, magne-

sium, iron and manganese). Garnet has a higher density

than sand.

gastroenteritis. An inflammation of the stomach and

intestine resulting in diarrhea, with vomiting and cramps

when irritation is excessive. When caused by an infectious

agent, it is often associated with fever.

gauge, pipe. A number that defines the thickness of the sheet

used to make steel pipe. The larger the number, the thinner

the pipe wall.

gavage. Type of exposure in which a substance is adminis-

tered to an animal through a stomach tube.

geological log. A detailed description of all underground

features discovered during the drilling of a well (depth,

thickness and type of formations).

geophysical log. A record of the structure and composition of

the earth encountered when drilling a well or similar type of

test hole or boring.

germicide (GERM-uh-SIDE). A substance formulated to kill

germs or microorganisms. The germicidal properties of

chlorine make it an effective disinfectant.

Giardia lamblia. Flagellate protozoan which is shed during

its cyst stage into the feces of man and animals. When

water containing these cysts is ingested, the protozoan

causes a severe gastrointestinal disease called giardiasis.

giardiasis (gee-are-DYE-us-sis). Intestinal disease caused

by an infestation of Giardia flagellates.

glass, pipe and fittings. The working pressure rating of a

specific pipe for use in water distribution systems which

includes allowances for surges. This term is used for cast

iron, ductile iron, asbestos cement and some plastic pipe.

gooseneck A portion of a service connection between the

distribution system water main and a meter. Sometimes

called a pigtail.

grab sample. A single sample collected at a particular time

and place which represents the composition of the water

only at that time and place.

grade. 1) The elevation of the invert of the bottom of a

pipeline. canal, culvert or similar conduit. 2) The inclination

or slope of a pipeline, conduit, stream channel, or natural

ground surface; usually expressed in terms of the ratio or

percentage of number of units of vertical rise or fall per unit

of horizontal distance. A 0.5 percent grade would be a drop

of one-half foot per hundred feet of pipe.

gram. A unit of mass equivalent to one milliliter of water at 4

degrees Celsius. 1/454 of a pound.

gravimetric. A means of measuring unknown concentrations

of water quality indicators in a sample by WEIGHING a

precipitate or residue of the sample.

grey water. Wastewater other than sewage, such as sink

drainage or washing machine discharge.

ground water. The supply of fresh water found beneath the

Earth's surface. usually in aquifers. which is often used for

supplying wells and springs. Because ground water is a

major source of drinking water there is growing concern

over areas where leaching agricultural or industrial pollut-

ants or substances from leaking underground storage tanks

are contaminating ground water.

ground water under the direct influence (UDI) of surface

water. Any water beneath the surface of the ground with: 1)

significant occurrence of Insects or other macroorganisms

algae. or large-diameter pathogens such as Giardia lamblia

or, 2) significant and relatively rapid shifts in water

characteristics such as turbidity, temperature, conductivity,

or pH which closely correlate to climatological or surface

water conditions. Direct influence must be determined for

individual sources in accordance with criteria established by

the State. The State determination of direct influence may

be based on site-specific measurements of water quality

and/or documentation of well construction characteristics

and geology with field evaluation.

gross alpha particle activity. The total radioactivity due to

alpha particle emission as inferred from measurements on a

dry sample.

gross beta particle activity. The total radioactivity due to

beta particle emission as inferred from measurements on a

dry sample.


half-life. The length of time required for the mass, concentra-

tion, or activity of a chemical or physical agent to be

reduced by one-half.

halogen. One of the chemical elements chlorine, bromine, or


hard water. Alkaline water containing dissolved salts that

interfere with some industrial processes and prevent soap

from lathering. Water may be considered hard if it has a

hardness greater than the typical hardness of water from the

region. Some textbooks define hard water as water with a

hardness of more than 100 mgAL as calcium carbonate.

hardness, water. A characteristic of water caused mainly by

the salts of calcium and magnesium, such as bicarbonate,

carbonate, sulfate, chloride and nitrate. Excessive hardness

in water is undesirable because it causes the formation of

soap curds, increased use of soap, deposition of scale in

boilers, damage in some industrial processes, and some-

times causes objectionable tastes in drinking water.

hazard evaluation. A component of risk assessment that

involves gathering and evaluating data on the types of

health injury or disease (e.g., cancer) that may be produced

by a chemical and on the conditions of exposure under

which injury or disease is produced.

head. The vertical distance (in feet) equal to the pressure (in

psi) at a specific point. The pressure head is equal to the

pressure in psi times 2.31 ft/psi.

head loss. The head, pressure or energy (they are the same)

lost by water flowing in a pipe or channel as a result of

turbulence caused by the velocity of the flowing water and

the roughness of the pipe, channel walls or restrictions

caused by fittings. Water flowing in a pipe loses head,

pressure or energy as a result of friction losses. Also see

friction losses.

header. A large pipe to which a series of smaller pipes are

connected. Also called a MANIFOLD.

heat sensor. A device that opens and closes a switch in

response to changes in the temperature. This device might

be a metal contact, or a thermocouple which generates a

minute electrical current proportional to the difference in

heat, or a variable resistor whose value changes in response

to changes in temperature. Also called a TEMPERATURE


heavy metals. Metallic elements with high atomic weights,

e.g., mercury, chromium, cadmium, arsenic, and lead. They

can damage living things at low concentrations and tend to

accumulate in the food chain.

hectare (HECK-tar). A measure of area in the metric system

similar to an acre. One hectare is equal to 10,000 square

meters and 2.4711 acres.

hematopoiesis. The production of blood and blood cells;


hepatic. Pertaining to the liver.

hepatitis (HEP-uh-TIE-this). Hepatitis is an inflammation of

the liver usually caused by an acute viral infection. Yellow

jaundice is one symptom of hepatitis.

hepatoma. A malignant tumor occurring in the liver.

herbicide (HERB-uh-SIDE). A compound, usually a man-

made organic chemical, used to kill or control plant growth.

hertz. The number of complete electromagnetic cycles or

waves in one second of an electrical or electronic circuit.

Also called the frequency of the current. Abbreviated Hz.

heterotrophic microorganisms. Bacteria and other microor-

ganisms that use organic matter synthesized by other

organisms for energy and growth.

heterotrophic plate count (HPC). The number of colonies

of heterotrophic bacteria grown on selected solid media at a

given temperature and incubation period, usually expressed

in number of bacteria per milliliter of sample.

high-line jumpers. Pipes or hoses connected to fire hydrants

and laid on top of the ground to provide emergency water

service for an isolated portion of a distribution system.

high-to-low-dose extrapolation. The process of prediction of

low exposure risks to rodents from the measured high

exposure-high risk data.

histology. The study of the structure of cells and tissues;

usually involves microscopic examination of tissue slices.

hose bib. Faucet. A location in a water line where a hose is


HTH (pronounce as separate letters). High Test Hypochlo-

rite. Calcium hypochlorite or Ca(OCl)2

human equivalent dose. A dose which, when administered

to humans, produces an effect equal to that produced by a

dose in animals.

human exposure evaluation. A component of risk assess-

ment that involves describing the nature and size of the

population exposed to a substance and the magnitude and

duration of their exposure. The evaluation could concern

past exposures, current exposures, or anticipated exposures.

human health risk. The likelihood (or probability) that a

given exposure or series of exposures may have or will

damage the health of individuals experiencing the expo-


humus. Organic portion of the soil remaining after prolonged

microbial decomposition.

hydrated lime. Limestone that has been burned and treated

with water under controlled conditions until the calcium

oxide portion has been converted to calcium hydroxide

(Ca(OH)2). Hydrated lime is quicklime combined with

water. CaO + H20 --> Ca(OH)2. Also see quicklime.

hydraulic grade line. The surface or profile of water flowing

of hydraulic gradient The slope of the hydraulic grade line.

is under pressure, the hydraulic grade line is at the level

water would rise to in a small vertical tube connected to the

pipe. Also see energy grade line

hydraulic gradient. The slope of the hydraulic grade line

This is the slope of the water surface in an open channel,

the slope of the water surface of the groundwater table, or

the slope of the water pressure for pipes under pressure.

hydrogeologic conditions. Conditions stemming from the

interaction of ground water and the surrounding soil and


hydrogeologic cycle. The natural process recycling water

from the atmosphere down to (and through) the earth and

back to the atmosphere again.

hydrogeology. The geology of ground water, with particular

emphasis on the chemistry and movement of water.

hydrogeologist (HI-dro-gee-ALL-uh-gist). A person who

studies and works with groundwater.

hydrograph. A graph of the rate of runoff plotted against

time for a point on a channel.

hydrologic cycle (HI-dro-LOJ-ick). Movement or exchange

of water between the atmosphere and the earth.

hydrology. The study of the occurrence, distribution and

circulation of the natural waters of the earth.

hydrolysis (hi-DROLL-uh-sis). A chemical reaction in

which a compound is converted into another compound by

taking up water.

hydrophilic (Hi-dro-FILL-ick). Having a strong affinity

(liking) for water. The opposite of hydrophobic.

hydrophobic (Hi-dro-FOE-bick). Having a strong aversion

(dislike) for water. The opposite of hydrophilic.

hydropneumatic (Hi-dro-new-MAT-ick). A water system,

usually small, in which a water pump is automatically

controlled (started and stopped) by the air pressure in a

compressed-air tank.

hydrostatic pressure (Hi-dro-STAT-ick). 1) The pressure at

a specific elevation exerted by a body of water at rest or, 2)

In the case of groundwater, the pressure at a specific

elevation due to the weight of water at higher levels in the

same zone of saturation.

hydrochlorination (Hi-poe-KLOR-uh-NAY-shun). The

application of hypochlorite compounds to water for the

purpose of disinfection.

hydrochlorinators (Hi-poe-KLOR-uh-NAY-tors). Chlorine

pumps, chemical feed pumps or devices used to dispense

chlorine solutions made from hypochlorites such as bleach

(sodium hypochlorite) or calcium hypochlorite into the

water being treated.

hypochlorite (Hi-poe-KLOR-ite). Chemical compounds

containing available chlorine; used for disinfection. They

are available as liquids (bleach) or solids (powder, granules

and pellets). Salts of hypochlorous acid.

hypolimnion (Hi-poe-LIM-knee-on). The lowest layer in a

thermally stratified lake or reservoir. This layer consists of

colder, more dense water, has a constant temperature and no

mixing occurs.


imhoff cone. A clear. cone-shaped container marked with

graduations. The cone is used to measure the volume of

settleable solids in a specific volume (usually one liter) of


impeller. A rotating set of vanes in a pump designed to pump

or lift water.

impermeable (im-PURR-me-uh-BULL). Not easily

penetrated. The property of a material or soil that des not

allow, or allows only with great difficulty, the movement or

passage of water.

incidence of tumors. Percentage of animals with tumors.

indicator (chemical). A substance that gives a visible

change, usually of color, at a desired point in a chemical

reaction, generally at a specified end point.

indicator (instrument). A device which indicates the result

of a measurement. Most indicators in the water utility field

use either a fixed scale and movable indicator (pointer) such

as a pressure gage or a movable scale and movable indica-

tor like those used on a circular-flow recording chart. Also

called a RECEIVER.

infiltration. 1) The gradual flow or movement of water into

and through (to percolate or pass through) the pores of the

soil. Also see percolation. 2) the penetration of water from

the soil into sewer or other pipes through defective joints,

connections or manhole walls.

infiltration gallery. A subsurface groundwater collection

system, typically shallow in depth, constructed with open-

jointed or perforated pipes that discharge collected water .

into a water-tight chamber. From this chamber the water is

pumped to treatment facilities and into the distribution

system. Infiltration galleries are usually located close to

streams or ponds and may be under the direct influence of

surface water.

infiltration rate. Quantity of water (usually measured in

inches) that will enter a particular type of soil per unit time

(usually one hour).

influent (IN-flu-ent). Water or other liquid-raw or partially

flowing INTO a reservoir, basin, treatment process

or treatment plant.

ingestion. Type of exposure through the mouth.

inhalation. Type of exposure through the lungs.

initial compliance period. The first full three-year compli-

ance period which begins at least 18 months after promul-


in-line filtration. The addition of chemical coagulants

directly to the filter inlet pipe. The chemicals are mixed by

the flowing water. Flocculation and sedimentation facilities

are eliminated. This pretreatment method is commonly used

in pressure filter installations. Also see conventional

filtration and direct filtration.

inorganic. Material such as sand, salt, iron, calcium salts and

other mineral materials. Inorganic substances are of mineral

origin, whereas organic substances are usually of animal or

plant origin. Also see organic.

input horsepower. The total power used in operating a pump

and motor.

Input HP = (Brake HP)(100%)Motor Efficiency, %)

insecticide. Any substance or chemical formulated to kill or

control insects.

in situ. In place, the original location, in the natural environ-


instream uses. Water uses that can be carried out without

removing the water from its source, as in navigation and


integrated exposure assessment. A summation over time, in

all media, of the magnitude of exposure to a toxic chemical.

integrator. A device or meter that continuously measures and

calculates (adds) total flows in gallons, or million cubic

feet. or some other unit of volume measurement. Also

called a TOTALIZER.

interface. The common boundary layer between two sub-

stances such as water and a solid (metal); or between two

fluids such as water and a gas (air); or between a liquid

(water) and another liquid (oil).

interflow. Lateral movement of water in the upper layer of


interlock An electrical switch, usually magnetically oper-

ated. Used to interrupt all (local) power to a panel or device

when the door is opened or the circuit exposed to service.

Internal friction. Friction within a fluid (water) due to

cohesive forces.

interspecies extrapolation model. Model used to extrapolate

from results observed in laboratory animals to humans.

Interstate carrier. Any vehicle or transport which conveys

passengers in interstate commerce.

interstice (in-TUR-stuhz). A very small open space in a rock

or granular material. Also called a void or void space. Also

see pore.

invert The lowest point of the channel inside a pipe, conduit,

or canal.

in vitro. In glass; a laboratory experiment performed in a test

tube or other vessel.

in vitro studies. Studies of-chemical effects conducted in

tissues, cells or subcellular extracts from an organism (i.e.,

not in the living organism).

in vivo. With in a living organism; a laboratory experiment

performed in which the substance under study is inserted

into a living organism.

in vivo studies. Studies of chemical effects conducted in

intact living organisms.

ion. An electrically charged atom, radical (such as SO42-), or

molecule formed by the loss or gain of one or more


ionic concentration. The concentration of any ion in solu-

tion, usually expressed in moles per liter.

ionization (EYE-on-uh-ZAY-shun). The splitting or

dissociation (separation) of molecules into negatively and

positively charged ions.

irreversible effect. Effect characterized by the inability of

the body to partially or fully repair injury caused by a toxic



jar test A laboratory procedure that simulates a water

treatment plant's coagulation/flocculation units with

differing chemical doses and also energy of rapid mix,

energy of slow mix, and settling time. The purpose of this

procedure is to ESTIMATE the minimum or ideal coagu-

lant dose required to achieve certain water quality goals.

Samples of water to be treated are commonly placed in six

jars. Various amounts of chemicals are added to each jar,

and the settling of solids is observed. The dose of

chemicals that provides satisfactory settling removal of

turbidity and/or color is the dose used to treat the water

being taken into the plant at that time. When evaluating the

results of a jar test, the operator should also consider the

floc quality in the flocculation area and the floc loading on

the filter.

jogging. The frequent starting and stopping of an electric


joule (jewel). A measure of energy, work or quantity of heat.

One joule is the work done when a force of one newton is

displaced a distance of one meter in the direction of force.


kilo. 1) Kilogram. 2) Kilometer. 3) A prefix meaning

"thousand" used in the metric system and other scientific

systems of measurement.

kinetic energy. Energy possessed by a moving body of

matter, such as water, as a result of its motion.

kjeldahl nitrogen (KELL-doll). Nitrogen in the form of

organic proteins or their decomposition product ammonia,

as measured by the Kjeldahl Method.


landfill Facility in which solid waste from municipal and/or

industrial sources is disposed; sanitary landfills are those

that are operated in accordance with environmental protec-

tion standards.

Langelier index (L.I.). An index reflecting the equilibrium pH

of a water with respect to calcium and alkalinity. This index

is used in stabilizing water to control both corrosion and the

deposition of scale.

Langelier index = pH - pHs

where pH = actual pH of the water, and pHs= pH at which

the water having the same alkalinity and calcium content is

just saturated with calcium carbonate.

large water system. A water system that serves more than

50,000 persons

latency. Time from the first exposure to a chemical until the

appearance of a toxic effect.

laundering weir (LAWN-der-ing weer). Sedimentation

basin overflow weir. A plate with V-notches along the top

to assure a uniform flow rate and avoid short-circuiting.

launders (LAWN-ders). Sedimentation basin and filter

discharge channels, consisting of overflow weir plates (in

sedimentation basins) and conveying troughs.

LC50. The concentration of a chemical in air or water which

is expected to cause death in 50% of test animals living in

that air or water.

LD50. The dose of a chemical taken by mouth or absorbed by

the skin which is expected to cause death in 50% of the test

animals so treated.

leachate. A liquid that results from water collecting contami-

nants as it trickles through wastes, agricultural pesticides or

fertilizers. Leaching may occur in farming areas, feedlots,

and landfills, and may result in hazardous substances

entering surface water, ground water, or soil.

leaching. The process by which soluble substances are

dissolved and transported down through the soil by re-


lead(Pb). A heavy metal that is hazardous to health if

breathed or swallowed. Its use in gasoline. paints, and

plumbing compounds has been sharply restricted or

eliminated by federal laws and regulations. See heavy


lead service line. A service line made of lead which connects

the water main to the building inlet and any lead pigtail,

gooseneck or other fitting which is connected to such lead


legionella. A genus of bacteria, some species of which have

caused a type of pneumonia called Legionnaires Disease.

lesion. A pathological or traumatic discontinuity of tissue or

loss of function of a part.

lethal. Deadly; fatal.

level controls. A float device (or pressure switch) which

senses changes in a measured variable and opens or closes a

switch in response to that change. In its simplest form, this

control might be a floating ball connected mechanically to a

switch or valve such as is used to stop water flow into a

toilet when the tank is full.

lifetime exposure. Total amount of exposure to a substance

that a human would receive in a lifetime (usually

assumed to be 70 years).

lindane (LYNN-dane). A pesticide that causes adverse

health effects in domestic water supplies and also is toxic to

freshwater and marine aquatic life.

linearity (LYNN-ee-AIR-it-ee). How closely an instrument

measures actual values of a variable through its effective

range; a measure used to determine the accuracy of an


linearized multistage model. Derivation of the multistage

model, where the data are assumed to be linear at low


littoral zone (LIT-or-al). 1)That portion of a body of fresh

water extending from the shoreline lakeward to the limit of

occupancy of rooted plants. 2) The strip of land along the

shoreline between the high and low water levels.

loading. The quantity of a substance entering the environ-

ment (soil, water, or air).

LOAEL Lowest-observed-adverse-effect level; the lowest

dose in an experiment which produced an observable

adverse effect.

logarithm (LOG-a-rith-m). The exponent that indicates the

power to which a number must be raised to produce a given

number. For example: if B2 = N, the 2 is the logarithm of N

(to the base B), or 102 =100 and log10 100 = 2. Also

abbreviated to "log."


macroscopic organisms (MACK-row-SKAWP-ick).

Organisms big enough to be seen by the eye without the aid

of a microscope.

malignant Very dangerous or virulent, causing or likely to

cause death.

managerial controls Methods of nonpoint source pollution

control that are derived from managerial decisions, such as

changes in application times or rates for agrochemicals.

manifold. A large pipe to which a series of smaller pipes are

connected. Also called a HEADER.

man-made beta particle and photon emitting All radionu-

clides emitting beta particles and/or photons listed in

Maximum Permissible Body Burdens and Maximum

Permissible Concentration of Radionuclides in Air or Water

for Occupational Exposure, NBS Handbook 69, except the

daughter products of thorium-232, uranium-235 and


manometer (man-NAH-mut-ter). An instrument for

measuring pressure. Usually, a manometer is a glass tube

filled with a liquid that is used to measure the difference in

pressure across a flow-measuring device such as an orifice

or Venturi meter. The instrument used to measure blood

pressure is a type of manometer.

margin of safety (MOS). Maximum amount of exposure

producing no measurable effect in animals (or studied

humans) divided by the actual amount of human exposure

in a population.

mathematical model. Model used during risk assessment to

perform extrapolations.

maximum contaminant level (MCL). The maximum

permissible level of a contaminant in water which is

delivered to the free flowing outlet of the ultimate user of a

public water system, except in the case of turbidity where

the maximum permissible level is measured at the point of

entry to the distribution system. Contaminants added to the

water under circumstances controlled by the user are

excluded from this definition, except those contaminants

resulting from the corrosion of piping and plumbing caused

by water quality.

maximum contaminant level goal (MCLG). The maximum

level of a contaminant in drinking water at which no known

or anticipated adverse effect on the health of persons would

occur, and which allows an adequate margin of safety.

Maximum contaminant level goals are non-enforceable

health goals .

maximum total trihalomethane potential (MTTP). The

maximum concentration of total trihalomethanes produced

in a given water containing a disinfectant residual, after 7

days at 25 degrees C or above.

MBAS. Methylene - Blue - Active Substances. These

substances are used in surfactants or detergents.

MCL See maximum contaminant level.

measured variable. A characteristic or component part that

is sensed and quantified (reduced to a reading of some kind)

by a primary element or sensor.

Mechanical joint A flexible device that joins pipes or

fittings together by the use of lugs and bolts.

medium-size water system. A water system that serves

greater than 3,300 and less than or equal to 50,000 person.

meg. A procedure used for checking the insulation resistance

on motors, feeders, buss bar systems, grounds, and branch

circuit wiring. Also see megger.

megger (from megohm). An instrument used for checking

the insulation resistance on motors, feeders, buss bar

systems, grounds, and branch circuit wiring. Also see MEG.

megohm. Meg means one million, so 5 megohms means 5

million ohms. A megger reads in millions of ohms.

meniscus (meh-NIS-cuss). The curved top of a column of

liquid (water, oil, mercury) in a small tube. When the liquid

wets the sides of the container (as with water), the curve

forms a valley. When the confining sides are not wetted (as

with mercury), the curve forms a hill or upward bulge.

mesh. One of the openings or spaces in a screen or woven

fabric. The value of the mesh is usually given as the number

openings per inch. This value does not consider the

diameter of the wire or fabric; therefore, the mesh number

does not always have a definite relationship to the size of

the hole.

mesotrophic (MESS-o-TRO-rick). Reservoirs and lakes

which contain moderate quantities of nutrients and are

moderately productive in terms of aquatic animal and plant


metabolism (meh-TAB-uh-LIZ-um). The sum of the

chemical reactions occurring within a cell or a whole

organism; includes the energy-releasing breakdown of

molecules (catabolism) and the synthesis of new molecules


metabolite. Any product of metabolism, especially a trans-

formed chemical.

metalimnion (MET-uh-LIM-knee-on). The middle layer in

a thermally stratified lake or reservoir. In this layer there is

a rapid decrease in temperature with depth. Also called the


metastatic. Pertaining to the transfer of disease from one

organ or part to another not directly connected with it.

methoxychlor (meth-OXY-klor). A pesticide which causes

adverse health effects in domestic water supplies and is also

toxic to freshwater and marine aquatic life. The chemical

name for methoxychlor is 2,2-bis (P-methoxyphenol)- 1, 1, I -


methyl orange alkalinity. A measure of the total alkalinity in

a water sample. The alkalinity is measured by the amount of

standard sulfuric acid required to lower the pH of the water

to a pH level of 4.5, as indicated by the change in color of

methyl orange from orange to pink. Methyl orange alkalin-

ity is expressed as milligrams per liter equivalent calcium


mg/L. See milligrams per liter.

microbial growth (my-KROW-bee-ul). The activity and

growth of microorganisms such as bacteria, algae, diatoms,

plankton and fungi.

microgram (pg). One-millionth of a gram (3.5 x 10-8 oz.

0.000000035 oz.).

micrograms per liter (mg/L) One microgram of a substance

dissolved in each liter of water. This unit is equal to parts

per billion (ppb) since one liter of water is equal in weight

to one billion micrograms.

micron (MY-kron). A unit of length. One millionth of a

meter or one thousandth of a millimeter. One micron equals

0.00004 of an inch.

microorganisms (MY-crow-OR-gan-IS-zums). Living

organisms that can be seen individually only with the aid of

a microscope.

mil A unit of length equal to 0.001 of an inch. The diameter

of wires and tubing is measured in mils, as is the thickness

of plastic sheeting .

milligram (mg). One-thousandth of a grain (3.5 x 10-1 oz.

0.000035 oz.).

milligrams per liter (mg/L). A measure of concentration of

a dissolved substance. A concentration of one mg/L means

that one milligram of a substance is dissolved in each liter

of water. For practical purposes, this unit is equal to parts

per million (ppm) since one liter of water is equal in weight

to one million milligrams. Thus a liter of water containing 10

milligrams of calcium has 10 parts of calcium per one

million parts of water, or 10 parts per million (10 ppm).

millimicron (MILL-uh-MY-kron). A unit of length equal to

10-3 microns (one thousandth of a micron), 10-6millimeters,

or 10-9 meters; correctly called a manometer, nm.

Million-gallons Per Day (MGD). A measure of water flow.

mineralization. The microbial conversion of an element

from an organic to an inorganic state.

modeling. Use of mathematical equations to simulate and

predict real events and processes.

molar or molarity. A molar solution consists of one gram

molecular weight of a compound dissolved in enough water

to make one liter of solution. A gram molecular weight is

the molecular weight of a compound in grains. For ex-

ample, the molecular weight of sulfuric acid (H2SO4) is 98.

A one M solution of sulfuric acid would consist of 98 grains

of H2SO4 dissolved in enough distilled water to make one

liter of solution.

mole. The molecular weight of a substance, usually expressed

in grains.

molecular weight. The molecular weight of a compound in

grams is the sum of the atomic weights of the elements in

the compound. The molecular weight of sulfuric acid

(H2SO4) in grams is 98.

Element Atomic Weight Number of Atoms Molecular Weight

H 1 2 2

S 32 1 32

0 16 4 64

molecule (MOLL-uh-KULE). The smallest division of a

compound that still retains or exhibits all the properties of

the substance.

monitoring. Measuring concentrations of substances in

environmental media or in human or other biological


monomer (MON-o-MER). A molecule of low molecular

weight capable of reacting with identical or different

monomers to form Polymers.

monomictic (mo-no-MICK-tick). Lakes and reservoirs

which are relatively deep, do not freeze over during the

winter months, and undergo a single stratification and

mixing cycle during the year. These lakes and reservoirs

usually become destratified during the mixing cycle, usually

in the fall of the year.

monovalent. Having a valence of one, such as the cuprous

(copper) ion, Cu+.

mortality. Death.

MOS. See margin of safety.

most probable number (MPN). MPN is the Most Probable

Number of coliform-group organisms per unit volume of

sample water. Expressed as the number of organisms per

100 mL off sample water.

motile (MO-till). Capable of self-propelled movement. A

term that is sometimes used to distinguish between certain

types of organisms found in water.

monitoring wells. Wells used to collect ground-water

samples for analysis to determine the amount, type, and

spread of contaminants In ground water.

motor efficiency. The ratio of energy delivered by a motor to

the energy supplied to it during a fixed period or cycle.

Motor efficiency ratings will vary depending upon motor

manufacturer and usually will range from 88.9 to 90.0


mudballs. Material that is approximately round in shape and

varies from pea-sized up to two or more inches in diameter.

This material forms in filters and gradually increases in size

when not removed by the backwashing process.

MPN See most probable number.

MTD. Maximum tolerated dose, the dose that an animal

species can tolerate for a major portion of its lifetime

without significant impairment or toxic effect other than


mulch. Any substance spread or allowed to remain on the

soil surface to conserve soil moisture and shield soil

particles from the erosive forces of raindrops and runoff.

multiple use. Use of land for more than one purpose; i.e.,

grazing of livestock, wildlife production. recreation,

watershed, and timber production. Could also apply to use

of bodies of water for recreational purposes, fishing, and

water supply.

multi-stage model Mathematical model based on the

multi-stage theory of the carcinogenic process, which yields

risk estimates either equal to or less than the one-hit model.

multi-stage pump. A pump that has more than one impeller

A single-stage pump has one impeller.

municipal sewage. Wastes (mostly liquid) originating from

a community; may be composed of domestic wastewaters

and/or industrial wastewaters.

mutagen. An agent that causes a permanent genetic change in

a cell other than that which occurs during normal genetic


mutagenicity. The capacity of a chemical or physical agent

to cause permanent alteration of the genetic material within

living cells.


N. See normal.

National Environmental Training Association (NETA). A

professional organization devoted to serving the environ-

mental trainer and promoting better operation of water-

works and pollution control facilities. For information on

NETA membership and publications, contact NETA, 8687

Via de Ventura, Suite 214, Scottsdale, AZ 85258

National Institute of Occupational Safety and Health. See


National Interim Primary Drinking Water Regulations.

Commonly referred to as NIPDWRs.

National Pollutant Discharge. Elimination System permit is

the regulatory agency document issued by either a federal

or state agency which is designed to control all discharges

of pollutants from point sources in U.S. waterways. NPDES

permits regulate discharges into navigable waters from all

point sources of pollution, including industries, municipal

treatment plants, large agricultural feed lots and return

Irrigation flows.

National Secondary Drinking Water Regulations. Com-

monly referred to as NSDWRs.

NCWS. See non-community water system.

near the first service connection. At one of the 20 percent

of all service connections in the entire system that are

nearest the water supply treatment facility, as measured by

water transport time within the distribution system.

necrosis. Death of cells or tissue.

nematodes. Roundworms, any of which are pathogenic for

plants and sometimes animals.

nephelometric (NEFF-el-o-MET-rick). A means of

measuring turbidity in a sample by using an instrument

called a nephelometer. A nephelometer passes light through

a sample and the amount of light deflected (usually at a 90-

degree angle) is then measured.

neoplasm. An abnormal growth or tissue, as a tumor.

nephelometric turbidity unit (NTU). The unit of measure

for turbidity.

NETA. See National Environmental Training Association.

neurotoxicity. Exerting a destructive or poisonous effect on

nerve tissue.

newton. A force which, when applied to a body having a

mass of one kilogram, gives it an acceleration of one meter

per second per second.

NIOSH The National Institute of Occupational Safety and

Health is an organization that tests and approves safety

equipment for particular applications. NIOSH is the

primary Federal agency engaged in research in the national

effort to eliminate on-the-job hazards to the health and

safety of working people. The NIOSH Publications Catalog

contains a listing of NIOSH publications mainly on

industrial hygiene and occupational health. To obtain a copy

of the catalog, write to National Technical Information

Service (NTIS), 5285 Port Royal Road, Springfield, VA

22161. NTIS Stock No. PB-86-116-787, price $45.95.

NIPDWR. National Interim Primary Drinking Water


nitrification. The biochemical transformation of ammonium

nitrogen to nitrate nitrogen.

nitrification inhibitor. A chemical that slows down the

conversion of ammonium to nitrate nitrogen.

nitrogen fixation. The biological or chemical process by

which elemental nitrogen, from the air, is converted to

organic or available nitrogen.

nitrogenous (nye-TRAH-jen-us). A term used to describe

chemical compounds (usually organic) containing nitrogen

in combined forms. Proteins and nitrates are nitrogenous


NOAEL No-observed-adverse-effect level; the highest dose

in an experiment which did not produce an observable

adverse effect.

noble metal Chemically inactive metal (such as gold). A

metal that does not corrode easily and is much scarcer (and

more valuable) than the so-called useful or base metals.

Also see base metal.

NOEL No-observed-effect level; dose level at which no

effects are noted.

nominal diameter. An approximate measurement of the

diameter of a pipe. Although the nominal diameter is used

to describe the size or diameter of a pipe, it is usually not

the exact inside diameter of the pipe.

non-community water system (NCWS). A public water

system that is not a community water system. There are

two types of NCWSs: transient and non-transient.

non-conventional pollutant Any pollutant which is not a

statutorily listed or which is poorly understood by the

scientific community.

non-ionic polymer (NON-eye-ON-ick). A polymer that has

no net electrical charge.

non-point source. Pollution sources which are diffuse and do

not have a single point of origin or are not introduced into a

receiving stream from a specific outlet. The pollutants are

generally carried off the land by stormwater runoff. The

commonly used categories for non-point sources are:

agriculture. forestry, urban, mining, construction, dams and

channels, land disposal, and saltwater intrusion.

non-potable (non-POE-tuh-bull). Water that may contain

objectionable pollution, contamination, minerals, or

infective agents and is considered unsafe and/or unpalatable

for drinking.

non-transient non-community water system (NTNCWS).

A public water system that regularly serves at least 25 of

the same nonresident persons per day for more than six

months per year.

normal. A normal solution contains one grain equivalent

weight of reactant (compound) per. liter of solution. The

equivalent weight of an acid is that weight which contains

one gram atom of ionizable hydrogen or its chemical

equivalent. For example, the equivalent weight of sulfuric

acid (H2SO4 is 49 (98 divided by 2 because there are two

replaceable hydrogen ions). A one N solution of sulfuric

acid would consist of 49 grains of H2SO4 dissolved in

enough water to make one liter of solution.

NPL National Priorities List; a list of Superfund sites

chosen for immediate attention.

NSDWR. National Secondary Drinking Water Regulations.

NTNCWS. See non-transient non-community water system.

NTP. National Toxicology Program.

nutrient Any substance that is assimilated (taken in) by

organisms and promotes growth. Nitrogen and phosphorous

are nutrients which promote the growth of algae. There are

other essential and trace elements which are also considered


nutrient pollution. Contamination of water resources by

excessive inputs of nutrients; insurface waters, excess algal

production is a major concern.


Occupational Safety and Health Act of 1970. See OSHA.

odor threshold. The minimum odor of a water sample that

can just be detected after successive dilutions with odorless

water. Also called THRESHOLD ODOR.

offstream uses. Water withdrawn from surface or ground

water sources for use at another place.

offset (or DROOP). The difference between the actual value

and the desired value (or set point); characteristic of

proportional controllers that do not incorporate reset action.

OHM The unit of electrical resistance. The resistance of a

conductor in which one volt produces a current of one


olfactory fatigue (oh-FAK-tore-ee). A condition in which a

person's nose, after exposure to certain odors, is no longer

able to detect the odor.

oligotrophic (AH-lig-o-TRO-flck). Reservoirs and lakes

which are nutrient poor and contain little aquatic plant or

animal life.

oncology. Study of cancer.

one-hit model Mathematical model based on the biological

theory that a single "hit" of some minimum critical amount

of a carcinogen at a cellular target- namely, DNA-can

initiate an irreversible series of events, eventually leading to

a tumor.

optimal corrosion control treatment The corrosion control

treatment that minimizes the lead and copper concentrations

at users' taps while insuring that the treatment does not

cause the water system to violate any national primary

drinking water regulations.

operation and maintenance costs. The ongoing, repetitive

costs of operating a water system; for example, employee

wages and costs for treatment chemicals and periodic

equipment repairs.

oral. Of the mouth; through or by the mouth.

organic. Substances that come from animal or plant sources.

Organic substances always contain carbon. (Inorganic

materials are chemical substances of mineral origin.) Also

see inorganic

organics. 1) A term used to refer to chemical compounds

made from carbon molecules. These compounds may be

natural materials (such as animal or plant sources) or man-

made materials (such as synthetic organics). Also see

organic. 2) Any form of animal or plant life. Also see


organism. Any form of animal or plant life. Also see


orifice (OR-uh-fiss). An opening (hole) in a plate, wall or

partition An orifice flange or plate placed in a pipe consists

of a slot or a calibrated circular hole smaller than the pipe

diameter. The difference in pressure in the pipe above and

at the orifice may be used to determine the flow in the pipe.

ORP. Oxidation-Reduction Potential. The electrical potential

required to transfer electrons from one compound or

element (the oxidant) to another compound or element (the

reductant); used as a qualitative measure of the state of

oxidation in water treatment systems.

orthotolidine (or-tho-TOL-uh-dine). Orthotolidine is a

calorimetric indicator of chlorine residual. If chlorine is

present, a yellow-colored compound is produced. This

reagent is no longer approved for chemical analysis.

OSHA (0-shuh). The Williams-Steiger Occupational Safety

and Health Act of 1970 (OSHA) is a law designed to

protect the health and safety of industrial workers and also

the operators of water supply systems and treatment plants.

OSHA also refers to the federal and state agencies which

administrator the OSHA regulations.

osmosis (oz-MOE-sis). The passage of a liquid from a weak

solution to a more concentrated solution across a semiper-

meable membrane. The membrane allows the passage of

the solvent (water) but not the dissolved solids (solutes).

This process tends to equalize the conditions on either side

of the membrane.

overall efficiency pump. The combined efficiency of a pump

and motor together. Also called the WIRE-TO-WATER


overdraft The pumping of water from a groundwater basin

or aquifer in excess of the supply flowing into the basin.

This pumping results in a depletion or "mining" of the

groundwater in the basin.

overflow rate. One of the guidelines for the design of settling

tanks and clarifiers in treatment plants. Used by operators to

determine if tanks and clarifiers are hydraulically (flow)

over- or underloaded. Also called SURFACE LOADING.

Overflow Rate (GDP/sq ft) = Flow (GPD)/Surface Area (sq ft)

overturn. The almost spontaneous mixing of all layers of

water in a reservoir or lake when the water temperature

becomes similar from top to bottom. This may occur in the

fall/winter when the surface waters cool to the same

temperature as the bottom waters and also in the spring

when the surface waters warms after the ice melts.

oxidation (ox-uh-DAY-shun). Oxidation is the addition of

oxygen, removal of hydrogen, or the removal of electrons

from an element or compound. In the environment, organic

matter is oxidized to more stable substances. The opposite

of reduction

oxidation-reduction potential. The electrical potential

required to transfer electrons from one compound or

element (the oxidant) to another compound or element (the

reductant); used as a qualitative measure of the state of

oxidation in water treatment systems.

oxidizing agent Any substance, such as oxygen (O2) or

chlorine (Cl2), that will readily add (take on) electrons. The

opposite is a reducing agent.

ozonation (O-zoe-NAY-shun). The application of ozone to

water for disinfection or for taste and odor control.


packed tower aeration. A method of treating water to

remove volatile organic chemical (VOCs) contaminants.

As water is mixed with air, VOCs move from water to air

which then passes through carbon filters to trap the con-


palatable (PAL-a-ta-ble). Water at a desirable temperature

that is free from objectionable tastes, odors, colors, and

turbidity. Pleasing to the senses.

parshall flume. A device used to measure the flow in an

open channel. The flume narrows to a throat of fixed

dimensions and then expands again. The rate of flow can be

calculated by measuring the difference in head (pressure)

before and at the throat of the flume.

particle count. The results of a microscopic examination of

treated water with a special "particle counter" which

classifies suspended particles by number and size.

particulate (par-TICK-you-let). A very small solid sus-

pended in water which can vary widely in size, shape,

density, and electrical charge. Colloidal and dispersed

particulates are artificially gathered together by the pro-

cesses of coagulation and flocculation.

partition coefficient. A measure of the extent to which a

pesticide is divided between the soil and ater phases.

parts per million (PPM). Parts per million parts, a measure-

ment of concentration on a weight or volume basis. This

term is equivalent to milligrams per liter (mg/L) which is

the preferred term.

Pascal. The pressure or stress of one newton per square

meter. (Abbreviated Pa)

1 psi = 6895 Pa = 6.895 kN/sq m = 0.0703 kg/sq cm

pathogenic organisms (path-o-JEN-ick). Organisms,

including bacteria, viruses or cysts, capable of causing

diseases (typhoid, cholera, dysentery) in a host (such as a

person). There are many types of organisms which do NOT

cause disease. These organisms are called non-pathogenic.

pathogens. Microorganisms that can cause disease in other

organisms or in humans, animals and plants. They may be

bacteria, viruses, or parasites and are found in sewage in

runoff from animal farms or rural areas populated with

domestic and/or wild animals, and in water used for

swimming. Fish and shellfish contaminated by pathogens,

or the contaminated water itself, can cause serious illnesses.

pathology. The study of disease.

percent saturation. The amount of a substance that is

dissolved in a solution compared with the amount that could

be dissolved in the solution, expressed as a percent.

Amount of substance that is dissolved x 100%

Amount that could be dissolved in solution

percolating water (PURR-co-LAY-ting). Water that passes

through soil or rocks under the force of gravity.

percolation (PURR-ko-LAY-shun). 1) The slow seepage of

water into and through the ground. 2) The slow passage of

water through a filter medium.

performance evaluation sample. A reference sample

provided to a laboratory for the purpose of demonstrating

that the laboratory can successfully analyze the sample

within limits of performance specified by the Agency. The

true value of the concentration of the reference material is

unknown to the laboratory at the time of the analysis.

periphyton (puh-RIF-uh-tawn). Microscopic plants and

animals that are firmly attached to solid surfaces under

water such as rocks, logs, pilings and other structures.

permeability. Generally used to refer to the ability of rock or

soil to transmit water.

permeate (PURR-me-ate). To penetrate and pass through, as

water penetrates and passes through soil and other porous


permissible dose. The dose of a chemical that may be

received by an individual without the expectation of a

significantly harmful result.

persistence. The resistance to degradation as measured by

the period of time required for complete decomposition of

a material.

person. An individual, corporation, company, association,

partnership; municipality; or State, Federal, or tribal


pesticide. Any substance or chemical designed or formulated

to kill or control weeds or animal pests. Also see algicide,

herbicide, insecticide and rodenticide.

petroleum derivatives. Chemicals formed when gasoline

breaks down in contact with ground water.

pH (pronounce as separate letters). pH is an expression of

the intensity of the basic or acid condition of a liquid.

Mathematically, pH is the logarithm (base 10) of the

reciprocal of the hydrogen ion concentration, [H+].

pH= Log (I/[H+])

The pH may range from 0 to 14, where 0 is most acid, 14

most basic, and 7 neutral. Natural waters usually have a pH

between 6.5 and 8.5.

pharmacokinetics. The dynamic behavior of chemicals

inside biological systems; it includes the processes of

uptake, distribution, metabolism, and excretion.

phenolic compounds (FEE-noll-LICK). Organic com-

pounds that are derivatives of benzene.

phenolphthalein alkalinity (FEE-nol-THAY-leen). The

alkalinity in a water sample measured by the amount of

standard acid required to lower the pH to a level of 8.3, as

indicated by the change in color of phenolphthalein from

pink to clear. Phenolphthalein alkalinity is expressed as

milligrams per liter equivalent calcium carbonate.

photosynthesis (foe-tow-SIN-thus-sis). A process in which

organisms, with the aid of chlorophyll (green plant en-

zyme), convert carbon dioxide and inorganic substances

into oxygen and additional plant material, using sunlight for

energy. All green plants grow by this process.

phytoplankton (Flo-tow-PANK-ton). Small, usually

microscopic plants (such as algae), found in lakes, reser-

voirs, and other bodies of water.

pico. A prefix used in the metric system and other scientific

systems of measurement which means 10-12 or


picocurie (pCi). A measure of radioactivity. One picocurie of

radioactivity is equivalent to 0.037 nuclear disintegrations

per second.

plan view. A diagram or photo showing a facility as it would

appear when looking down on top of it.

plankton. 1) Small, usually microscopic, plants (phytoplank-

ton) and animals (zooplankton) in aquatic systems. 2) All of

the smaller floating, suspended or self-propelled organisms

in a body of water.

plug flow. A type of flow that occurs in tanks, basins or

reactors when a slug of water moves through a tank without

ever dispersing or mixing with the rest of the water flowing

through the tank.

plumes. The way polluted water extends downstream from

the pollution source (analogous to smoke from a smoke-

stack as it drifts downwind in the atmosphere).

point of disinfectant application. The point where disinfec-

tant is applied and water downstream of that point is not

subject to recontamination by surface water runoff.

point-of-entry treatment device. A treatment device applied

to the drinking water entering a house or building for the

purpose of reducing contaminants in the drinking water

distributed throughout the house or building .

point-of-use treatment device. A treatment device applied to

a single tap used for the purpose of reducing contaminants

in drinking water at that one tap.

point source. A stationery location or fixed facility from

which pollutants are discharged or emitted. Also, any single

identifiable source of pollution, e.g., a pipe, ditch, ship, ore

pit, factory smokestack.

pole shader. A copper bar circling the laminated iron core

inside the coil of a magnetic starter.

pollutant. Generally, any substance introduced into the

environment that adversely affects the usefulness of a


pollution. Generally, the presence of matter or energy whose

nature, location or quantity produces undesired environmen-

tal effects. Under the Clean Water Act, for example, the

term is defined as the man-made or man-induced alteration

of the physical, biological, and radiological integrity of


polyelectrolyte (POLLY-ee-LECK-tro-lite). A high-

molecular-weight (relatively heavy) substance having points

of positive or negative electrical charges that is formed by

either natural or man-made processes. Natural polyelectro-

lytes may be of biological origin or derived from starch

products and cellulose derivatives. Man-made polyelectro-

lytes consist of simple substances that have been made into

complex substances of high molecular weight. Used with

other chemical coagulants to aid in binding small suspended

particles to larger chemical flocs for their removal from

water. Often called a polymer.

polymer. A chemical formed by the union of many mono-

mers (a molecule of low molecular weight). Polymers are

used with other chemical coagulants to aid in binding small

suspended particles to larger chemical flocs for their

removal from water. All polyelectrolytes are polymers, but

not all polymers are polyelectrolytes.

population at risk. A population subgroup that is more likely

to be exposed to a chemical, or is more sensitive to a

chemical, than is the general population.

pore. A very small open space in a rock or granular material.

Also see interstice

porosity. the capacity of soil of rock to hold water.

positive displacement pump. A type of piston, diaphragm,

gear or screw pump that delivers a constant volume with

each stroke. Positive displacement pumps are used as

chemical solution feeders.

postchlorination. The addition of chlorine to the plant

effluent, FOLLOWING plant treatment, for disinfection


potency. Amount of material necessary to produce a given

level of a deleterious effect.

potentiation. The effect of one chemical to increase the

effect of another chemical.

potentiometric surface. The level to which water will rise in

cased wells or other cased excavations into aquifers,

measured as feet above mean sea level.

potable water. Water that is safe and satisfactory for

drinking and cooking.

power factor. The ratio of the true power passing through an

electric circuit to the product of the voltage and amperage

in the circuit. This is a measure of the lag or load of the

current with respect to the voltage.

ppb. Parts per billion. Also pg/L or micrograms per liter.

ppm. Parts per million. Also mg/L or milligrams per liter.

prechlorination. The addition of chlorine at the headworks

of the plant PRIOR TO other treatment processes mainly

for disinfection and control of tastes, odors and aquatic

growths. Also applied to aid in coagulation and settling.

precipitate (pre-SIP-uh-TATE). 1) An insoluble, finely

divided substance which is a product of a chemical reaction

within a liquid. 2) The separation from solution of an

insoluble substance.

precipitation (pre-SIP-uh-TAY-shun). 1) The process by

which atmospheric moisture falls onto a land or water

surface as rain, snow, hail, or other forms of moisture. 2)

The chemical transformation of a substance in solution into

an insoluble form (precipitate).

Precision. The ability of an instrument to measure a process

variable and to repeatedly obtain the same result. The

ability of an instrument to reproduce the same results.

precursor, THM (pre-CURSE-or). Natural organic com-

pounds found in all surface and groundwaters. These

compounds MAY react with halogens (such as chlorine) to

form trihalomethanes (try-HAL-o-METH-hanes) (THMs);

they MUST be present in order for THMs to form.

prescriptive (pre-SKRIP-tive). Water rights which are

acquired by diverting water and putting it to use in accor-

dance with specified procedures. These procedures include

filing a request to use unused water in a strewn, river or

lake with a state agency.

pressure control. A switch which operates on changes in

pressure. Usually this is a diaphragm pressing against a

spring. When the force on the diaphragm overcomes the

spring pressure, the switch is actuated (activated).

pressure head. The vertical distance (in feet) equal to the

pressure (in psi) at a specific point. The pressure head is

equal to the pressure in psi times 2.31 ft/psi.

prevalence study. An epidemiological study which examines

the relationships between diseases and exposures as they

exist in a defined population at a particular point in time.

primacy. The responsibility for ensuring that a law is

implemented, and the authority to enforce a law and related

regulations. A primacy agency has the primary responsibil-

ity for administrating and enforcing regulations.

primary element. An instrument which measures (senses) a

physical condition or variable of interest. Floats and

thermocouples are examples of primary elements. Also

called a sensor.

prime. The action of filling a pump casing with water to

remove the air. Most pumps must be primed before startup

or they will not pump any water.

prior appropriation. A doctrine of water law that allocates

the right to use water on a first-come first-serve basis.

process variable. A physical or chemical quantity which is

usually measured and controlled in the operation of a water

treatment plant or an industrial plant.

product water. Water that has passed through a water

treatment plant. All the treatment processes are completed

or finished. This water is the product from the water

treatment plant and is ready to be delivered to the consum-

ers. Also called finished water.

profile. A drawing showing elevation plotted against dis-

tance, such as the vertical section or side view of a pipeline.

prospective study. An epidemiological study which exam-

ines the development of disease in a group of persons

determined to be presently free of the disease.

prussian blue. A blue paste or liquid (often on a paper like

carbon paper) used to show a contact area. Used to deter-

mine if gate valve seats fit properly.

PSIG. Pounds per Square Inch Gage pressure. The pressure

within a closed container or pipe measured with a gage in

pounds per square inch. See gage pressure.

public water system. A system for the provision to the

public of piped water for human consumption, If such

system has at least fifteen service connections or regularly

least 60 days out of the year. Such term includes: 1) any

collection, treatment, storage, and distribution facilities

under control of the operator of such system and used

primarily in connection with such system, and 2) any

collection or pretreatment storage facilities not under such

control which are used primarily in connection with such

system. A public water system is either a "community water

system" or a "non-community water system.'

pumping station. Mechanical devices installed in sewer or

water systems or other liquid-carrying pipelines that move

the liquids to a higher level.

pumping water level. The vertical distance in feet from the

centerline of the pump discharge to the level of the free

pool while water is being drawn from the pool.

purveyor, water (purr-VAY-or). An agency or person that

supplies water (usually potable water).

putrefaction (PEW-truh-FACK-shun). Biological decom-

position of organic matter, with the production of ill-

smelling and tasting products, associated with anaerobic (no

oxygen present) conditions.


qualitative. Descriptive of kind, type or direction, as opposed

to size, magnitude or degree.

quantitative. Descriptive of size, magnitude or degree.

quicklime. A material that is mostly calcium oxide (CaO) or

calcium oxide in natural association with a lesser amount of

magnesium oxide. Quicklime is capable of combining with

water to form hydrated lime. Also see hydrated lime.


radial to impeller. Perpendicular to the impeller shaft.

Material being pumped flows at a right angle to the impel-


radical. A group of atoms that is capable of remaining

unchanged during a series of chemical reactions. Such

combinations (radicals) exist in the molecules of many

organic compounds; sulfate (SO42-) is an inorganic radical.

radionuclide. Any man-made or natural element which emits

radiation in the form of alpha or beta particles, or as gamma


range. The spread from minimum to maximum values that an

instrument is designed to measure. Also see span and

effective range.

ranney collector. This water collector is constructed as a dug

well from 12 to 16 feet (3.5 to 5 m) in diameter that has

been sunk as a caisson near the bank of a river or lake.

Screens are driven radially and approximately horizontally

from this well into the sand and the gravel deposits underly-

ing the river.

raw water. 1) Water in its natural state, prior to any treat-

ment. 2) Usually the water entering the first treatment

process of a water treatment plant.

reaeration (RE-air-A-shun). The introduction of air through

forced air diffusers into the lower layers of the reservoir. As

the air bubbles form and rise through the water, oxygen

from the air dissolves into the water and replenishes the

dissolved oxygen. The rising bubbles also cause the lower

waters to rise to the surface where oxygen from the

atmosphere is transferred to the water. This is sometimes

called surface reaeration.

reagent (re-A-gent). A pure chemical substance that is used

to make new products or is used in chemical tests to

measure, detect, or examine other substances.

recarbonation (re-CAR-bun-NAY-shun). A process in

which carbon dioxide is bubbled into the water being

treated to lower the pH. The pH may also be lowered by the

addition of acid. Recarbonation is the final stage in the

lime-soda ash softening process. This process converts

carbonate ions to bicarbonate ions and stabilizes the

solution against the precipitation of carbonate compounds.

receiver. A device which indicates the result of a measure-

ment. Most receivers in the water utility field use either a

fixed scale and movable indicator (pointer) such as pressure

gage or a movable scale and movable indicator like those

used on a circular-flow recording chart. Also called an


receiving waters. All distinct bodies of water that receive

runoff or wastewater discharges, such as streams, rivers,

ponds, lakes, and estuaries.

receptor. 1) In biochemistry: a specialized molecule in a cell

that binds a specific chemical with high specificity and high

affinity. 2) In exposure assessment: an organism that

receives, may receive, or has received environmental

exposure to a chemical.

recharge. Process by which rain water (precipitation) seeps

into the ground-water system.

recharge area. Generally, an area that is connected with the

underground aquifer(s) by a highly porous soil or rock

layer. Water entering a recharge area may travel for miles


recharge rate. The quantity of water per unit time that

replenishes or refills an aquifer.

recorder. A device that creates a permanent record, on a

paper chart or magnetic tape, of the changes of some

measured variable.

reducing agent. Any substance, such as base metal (iron) or

the sulfide ion (S2-), that will readily donate (give up)

electrons. The opposite is an oxidizing agent.

reduction (re-DUCK-shun). Reduction is the addition of

hydrogen, removal of oxygen, or the addition of electrons to

an element or compound. Under anaerobic conditions (no

dissolved oxygen present), sulfur compounds are reduced to

odor-producing hydrogen sulfide (H2S and other com-

pounds. The opposite of oxidation.

reference. A physical or chemical quantity whose value is

known exactly, and thus is used to calibrate or standardize


reliquifaction (re-LICK-we-FACK-shun).

rem. The unit of dose equivalent from ionizing radiation to

the total body or any internal organ or organ system. A

millirem (mrem)" is 1/1000 of a rem.

renal Pertaining to the kidney.

repeat compliance period. Any subsequent compliance

period after the initial compliance period.

representative sample. A portion of material or water that is

as nearly identical in content and consistency as possible to

that in the larger body of material or water being sampled.

reservoir. Any natural or artificial holding area used to store;

regulate, or control water.

residual chlorine. The amount of free and/or available

chlorine remaining after a given contact time under speci-

fied conditions.

residual disinfectant concentration ("C" in CT calcula-

tions). The concentration of disinfectant measured in mg/L

in a representative sample of water.

residue. The dry solids remaining after the evaporation of a

sample of water or sludge. Also see total dissolved solids

respiration. The process in which an organism uses oxygen

for its life processes and gives off carbon dioxide.

retrospective study. An epidemiological study which

compares diseased persons with non-diseased persons and

works back in time to determine exposures.

reverse osmosis (oz-MOE-sis). The application of pressure

to a concentrated solution which causes the passage of a

liquid from the concentrated solution to a weaker solution

across a semipermeable membrane. The membrane allows

the passage of the solvent (water) but not the dissolved

solids (solutes). The liquid produced is a demineralized

water. Also see osmosis.

reversible effect. An effect which is not permanent, espe-

cially adverse effects which diminish when exposure to a

toxic chemical is ceased.

RfD (Reference dose). The daily exposure level which,

during an entire lifetime of a human, appears to be without

appreciable risk on the basis of all facts known at the time.

Same as ADI.

rill. A small channel eroded into the soil surface by runoff,

rills easily can be smoothed out (obliterated) by normal


riparian rights. A doctrine of state water law under which a

land owner is entitled to use the water on or bordering his

property, including the right to prevent diversion or misuse

of upstream waters. Riparian land is land that borders on

surface water.

risk. The potential for realization of unwanted adverse

consequences or events.

risk assessment. A qualitative or quantitative evaluation of

the environmental and/or health risk resulting from expo-

sure to a chemical or physical agent (pollutant); combines

exposure assessment results with toxicity assessment results

to estimate risk.

risk characterization. Final component of risk assessment

that involves integration of the data and analysis involved in

hazard evaluation, dose-response evaluation, and human

exposure evaluation to determine the likelihood that humans

will experience any of the various forms of toxicity

associated with a substance.

risk estimate. A description of the probability that organisms

exposed to a specified dose of chemical will develop an

adverse response (e.g., cancer).

risk factor. Characteristic (e.g., race, sex, age, obesity) or

variable (e.g., smoking, occupational exposure level)

associated with increased probability of a toxic effect.

risk management. Decisions about whether an assessed risk

is sufficiently high to present a public health concern and

about the appropriate means for control of a risk judged to

be significant.

risk specific dose. The dose associated with a specified risk


rodenticide (row-DENT-uh-SIDE). Any substance or

chemical used to kill or control rodents.

rotameter (RODE-uh-ME-ter). A device used to measure

the flow rate of gases and liquids. The gas or liquid being

measured flows vertically up a tapered, calibrated tube.

Inside the tube is a small ball or bullet-shaped float (it may

rotate) that rises or falls depending on the flow rate. The

flow rate may be read on a scale behind or on the tube by

looking at the middle of the ball or at the widest part or top

of the float.

rotor. The rotating part of a machine. The rotor is surrounded

by the stationary (non-moving) parts (stator) of the ma-


route of exposure. The avenue by which a chemical comes

into contact with an organism (e.g., inhalation, ingestion,

dermal contact, injection).

run-off. That part of precipitation, snow melt, or irrigation

water that runs off the land into streams or other surface

water. It can carry pollutants from the air and land into the

receiving waters.

saturation. The condition of a liquid (water) when it has


sacrificial anode. An easily corroded material deliberately

installed in a pipe or tank. The intent of such an installation

is to give up (sacrifice) this anode to corrosion while the

water supply facilities remain relatively corrosion free.

safe. Condition of exposure under which there is a "practical

certainty" that no harm will result in exposed individuals.

Safe Drinking Water Act (SDWA). Commonly referred to

as SDWA. An Act passed by the U.S. Congress in 1974.

The Act establishes a cooperative program among local,

state and federal agencies to insure safe drinking water for


safe water. Water that does not contain harmful bacteria, or

toxic materials or chemicals. Water may have taste and

odor problems, color and certain mineral problems and still

be considered safe for drinking.

safe yield . The annual quantity of water that can be taken

from a source of supply over a period of years without

depleting the source beyond its ability to be replenished

naturally in "wet years".

salinity. 1)The relative concentration of dissolved salts,

usually sodium chloride, in a given water.. 2) A measure of

the concentration of dissolved mineral substances in water.

sand. Soil particles between 0.05 and 2 .0 mm in diameter.

sand filters. Devices that remove some suspended solids

from sewage. Air and bacteria decompose additional wastes

filtering through the sand so that cleaner water drains from

the bed.

sanitary sewer. A sewer that transports only wastewaters

(from domestic residences and/or industries) to a wastewa-

ter treatment plant.

sanitary survey. An on-site review of the water source,

facilities, equipment, operation, and maintenance of a

public water system for the purpose of evaluating the

adequacy of the facilities for producing and distributing safe

drinking water.

saprophytes (SAP-row-FIGHTS). Organisms living on dead

or decaying organic matter. They help natural decomposi-

tion of organic matter in water.

saturated zone. The area below the water table where all

open spaces are filled with water.

saturator (SAT-you-RAY-tore). A device which produces a

fluoride solution for the fluoridation process. The device is

usually a cylindrical container with granular sodium

fluoride on the bottom. Water flows either upward or

downward through the sodium fluoride to produce the

fluoride solution.

schedule, pipe. A sizing system of arbitrary numbers that

specifies the I.D. (inside diameter) and O.D. (outside

diameter) for each diameter pipe. This term is used for

steel, wrought iron, and some types of plastic pipe. Also

used to describe the strength of some types of plastic pipe.

SCD (SWCD). Soil Conservation District (also called Soil

and Water Conservation District in some areas); a local

government entity with in a defined water or soil protection

area tat provides assistance to farmers and other local

residents in conserving natural resources, especially soil and


SCFM. Cubic Feet of air per Minute at Standard conditions

of temperature, pressure and humidity (O degrees C /14.7

psia /50% relative humidity).

SCS. Soil Conservation Service. An agency of the United

States Department of Agriculture that provides technical

assistance for resource conservation to farmers, other

Federal, state and local agencies, and to local soil conserva-

tion districts.

SDWA. See Safe Drinking Water Act.

secchi disc (SECK-key). A flat, white disc lowered into the

water by a rope until it is just barely visible. At this point,

the depth of the disc from the water surface is the recorded

Secchi disc transparency.

seepage. The percolation of water through the soil from

unlined channels, ditches, watercourses and water storage


sedimentation. A water treatment process in which solid

particles settle out of the water being treated in a large

clarifier or sedimentation basin .

sediment yield. The quantity of sediment arriving at a

specific location.

seize up. Seize up occurs when an engine overheats and a

part expands to the point where the engine will not run.

Also called "freezing".

semi-confined aquifer. An aquifer that is partially confined

by a soil layer (or layers) of low permeability through

which recharge and discharge can occur.

sensor. An instrument that measure (senses) a physical

condition or variable of interest. Floats and thermocouples

are examples of sensors. Also called a primary element

septage. The liquid and semisolid contents removed by

pumping from a septic tank.

septic (SEP-tick). A condition produced by bacteria when all

oxygen supplies are depleted. If severe, bottom deposits and

water turn black, give off foul odors, and the water has a

greatly increased chlorine demand.

septic system. An onsite system designed to treat and

dispose of domestic sewage; a typical septic system consists

of a tank that receives wastes from a residence or business

And a system of tile lines or a pit for disposal of the liquid

effluent that remains after decomposition of the solids by

bacteria in the tank.

sequestration (SEE-kwes-TRAY-shun). A chemical

completing (forming or joining together) of metallic

cations (such as iron) with certain inorganic compounds,

such as phosphate. Sequestration prevents the precipitation

of the metals (iron). Also see chelation.

service line sample. A one-liter sample of water collected 'm

accordance with CFR Section 141.86(b)(6)of the code of

Federal Regulations, that has been standing for a least 6

hours in a service line.

service pipe. The pipeline extending from the water main to

the building served or to the consumers system.

set point. The position at which the control or controller is

set. This is the same as the desired value of the process


sewage. The used water and solids that flow from homes

through sewers to a wastewater treatment plant. The

preferred term is WASTEWATER.

sewage. Liquid and solid wastes carried in sewers.

sewer. An underground system of conduits (pipes and/or

tunnels) that collect and transport wastewaters and/or

runoff; gravity sewers carry free-flowing water and wastes;

pressurized sewers carry pumped wastewaters under


sewerage system. The network of sewers that carries sewage

from point of origin to point of treatment.

shock load. The arrival at a water treatment plant of raw

water containing unusual amounts of algae, colloidal

matter, color, suspended solids, turbidity, or other pollut-


short-circuiting. A condition that occurs in tanks or basins

when some of the water travels faster than the rest of the

flowing water. This is usually undesirable since it may

result in shorter contact, reaction, or settling times in

comparison with the theoretical (calculated) or presumed

detention times.

silt. Soil particles between 0.05 and 0.002 millimeter in

approximate diameter.

simulate. To reproduce the action of some process, usually

on a smaller scale.

single family structure. A building constructed as a single-

family residence that is currently used as either a residence

or a place of business.

single-stage pump. A pump that has only one impeller. A

multi-stage pump has more than one impeller.

sink. A place in the environment where a compound or

material collects. See reservoir.

slake. To mix with water with a true chemical combination

(hydrolysis) taking place, such as in the slaking of lime.

slope. The slope or inclination of a trench bottom or a trench

side wall is the ratio of the vertical distance to the horizon-

tal distance or "rise over run." Also see grade (2).

slow sand filtration. A process involving passage of raw

water through a bed of sand at low velocity (generally less

than 0.4 m/h) resulting in substantial particulate removal by

physical and biological mechanisms.

sludge (sluj). The settleable solids separated from water

during processing.

slurry (SLUR-e). A watery mixture or suspension of

insoluble (not dissolved) matter; a thin watery mud or any

substance resembling it (such as a grit slurry or a lime


SMCLs. Secondary Maximum Contaminant Levels. Second-

ary MCLs for various water quality indicators are estab-

lished to protect public welfare.

SNARL Suggested No Adverse Response Level. The

concentration of a chemical in water that is expected not to

cause an adverse health effect.

soft water. Water having a low concentration of calcium and

magnesium ions. According to U.S. Geological Survey

guidelines, soft water is water having a hardness of 60

milligrams per liter or less.

software programs. Computer programs; the list of instruc-

tions that tell a computer how to perform a given task or


soil erodibility. A measure of the soil's susceptibility to

raindrop impact, runoff and other erosional processes.

soil profile. A vertical section of the earth's highly weathered

upper surface often showing several distinct layers, or


soil structure. The arrangement of soil particles into


soil texture. The proportions of soil particles (sand, silt, and

clay) in a soil profile.

solder. A metallic compound used to seal the joints between

pipes. Until recently, most solder contained 50 percent lead.

The use of lead solder containing more than 0.2% lead is

now prohibited for pipes carrying potable water.

sole source aquifer. An aquifer that supplies 50 percent or

more of the drinking water of an area.

solenoid (SO-luh-noid). A magnetically (electrical coil)

operated mechanical device. Solenoids can operate a small

valve or a switch.

solution. A liquid mixture of dissolved substances. In a

solution it is impossible to see all the separate parts.

sorption. A surface phenomenon which may be either

absorption or adsorption, or a combination of the two; often

used when the specific mechanism is not known.

span. The scale or range of values an instrument is designed

to measure. Also see range.

specific conductance. A rapid method of estimating the

dissolved-solids content of a water supply. The measure-

ment indicates the capacity of a sample of water to carry an

electrical current, which is related to the concentration of

ionized substances in the water. Also called conductance.

specific gravity. Weight of a particle, substance, or chemical

solution in relation to the weight of water. Water has a

specific gravity of 1.000 at 4 degrees C (39 degrees F).

Particulates in raw water may have a specific gravity of

1.005 to 2.5.

specific yield. The quantity of water that a unit volume of

saturated permeable rock or soil will yield when drained by

gravity. Specific yield may be expressed as a ratio or as a

percentage by volume.

spoil Excavated material such as soil from the trench of a

water main.

spore. The reproductive body of an organism which is

capable of giving rise to a new organism either directly or

indirectly. A viable (able to live and grow) body regarded

as the resting stage of an organism. A spore is usually more

resistant to disinfectants and heat than most organisms.

spring. Ground water seeping out of the earth where the

water table intersects the ground surface.

spring line. Theoretical center of a pipeline. Also, the

guideline for laying a course of bricks.

standard. A physical or chemical quantity whose value is

known exactly, and is used to calibrate or standardize

instruments. Also see reference.

Standard Method See Standard Methods for the Examina-

tion of Water and Wastewater.

Standard Methods for the Examination of Water and

Wastewater. A joint publication of the American Public

Health Association, American Water Works Association,

and the Water Pollution Control Federation which outlines

the procedures used to analyze the impurities in water and


standard sample. The aliquot of finished drinking water that

is examined for the presence of coliform bacteria.

standard solution. A solution in which the exact concentra-

tion of a chemical or compound is known.

standardize. To compare with a standard. 1) In wet chemis-

try, to find out the exact strength of a solution by comparing

it with a standard of known strength. 2) To set up an

instrument or device to read a standard. This allows you to

adjust the instrument so that it reads accurately, or enables

you to apply a correction factor to the readings.

starters. Devices used to start up large motors gradually to

avoid severe mechanical shock to a driven machine and to

prevent disturbance to the electrical lines (causing dimming

and flickering of lights).

State. The agency of the State or Tribal government which

has jurisdiction over public water systems. During any

period when a State or Tribal government does not have

primary enforcement responsibility pursuant to Section

1413 of the Safe Drinking Water Act, the term "State"

means the Regional Administrator, U.S. Environmental

Protection Agency.

static head. When water is not moving, the vertical distance

(in feet) from a specific point to the water surface is the

static head. (The static pressure in psi is the static head in

feet times 0.433 psi/ft.) Also see dynamic pressure and

static pressure

static pressure. When water is not moving, the vertical

distance (in feet) from a specific point to the water surface

is the static head. The static pressure in psi is the static head

in feet times 0.433 psi/ft. Also see dynamic pressure and

static head

static water depth. The vertical distance in feet from the

centerline of the pump discharge down to the surface level

of the free pool while no water is being drawn from the

pool or water table.

static water level. 1) The elevation or level of the water table

in a well when the pump is not operating. 2) The level or

elevation to which water would rise in a tube connected to

an artesian aquifer, or basin, or conduit under pressure.

stator. That portion of a machine which contains the station-

ary (non-moving) parts that surround the moving parts


sterilization (STARE-uh-luh-ZAY-shun). The removal or

destruction of all microorganisms, including pathogenic and

other bacteria, vegetative forms and spores. Compare with


stethoscope. An instrument used to magnify sounds and

convey them to the ear.

strip cropping. A crop production system that involves

planting alternating strips of row crops and close-growing

forage crops; the forage strips intercept and slow runoff

from the less protected row crop strips.

stochastic. Based on the assumption that the actions of a

chemical substance results from probabilistic events.

storm sewer. A sewer that collects and transports surface

runoff to a discharge point (infiltration basin, receiving

stream, treatment plant).

stratification. The formation of separate layers (of tempera-

ture, plant, or animal life) in a lake or reservoir. Each layer

has similar characteristics such as all water in the layer has

the same temperature. Also see thermal stratification.

subchronic. Of intermediate duration, usually used to

describe studies or levels of exposure between 5 and 90


submergence. The distance between the water surface and

the media surface in a filter.

submerged aquatic vegetation (SAV). Aquatic vegetation,

such as sea grasses, that cannot withstand excessive drying

and therefore live with their leaves at or below the water

surface. SAVs provide an important habitat for young fish

and other aquatic organisms.

suction lift The NEGATIVE pressure [in feet (meters) of

water or inches (centimeters) of mercury vacuum] on the

suction side of the pump. The pressure can be measured

from the centerline of the pump DOWN TO (lift) the

elevation of the hydraulic grade line on the suction side of

the pump.

superchlorination (SUE-per-KLOR-uh-NAY-shun).

Chlorination with doses that are deliberately selected to

produce free or combined residuals so large as to require

dechlorination .

Superfund. Federal law which authorizes EPA to manage

the clean-up of abandoned or uncontrolled hazardous waste


supernatant (sue-per-NAY-tent). Liquid removed from

settled sludge. Supernatant commonly refers to the liquid

between the sludge on the bottom and the water surface of a

basin or container.

supersaturated. An unstable condition of a solution (water)

in which the solution contains a substance at a concentration

greater than the saturation concentration for the substance.

supplier of water. Any person who owns or operates a public

water system.

surface loading. One of the guidelines for the design of

settling tanks and clarifiers in treatment plants. Used by

operators to determine if tanks and clarifiers are hydrauli-

cally (flow) over- or underloaded. Also called overflow


surface pump. A mechanism for removing water or waste-

water from a sump or wet well.

surface runoff. Precipitation, snow melt, or irrigation in

excess of what can infiltrate the soil surface and be stored in

small surface depressions; runoff is a major transporter of

non-point source pollutants.

surface water. All water naturally open to the atmosphere

(rivers, lakes. reservoirs, streams, impoundments, seas,

estuaries, etc.) and all springs. wells, or other collectors

which are directly influenced by surface water.

surfactant (sir-FAC-tent). Abbreviation for surface-active

agent. The active agent in detergents that possesses a high

cleaning ability.

surge chamber. A chamber or tank connected to a pipe and

located at or near a valve that may quickly open or close or

a pump that may suddenly start or stop. When the flow of

water in a pipe starts or stops quickly, the surge chamber

allows water to flow into or out of the pipe and minimize

any sudden positive or negative pressure waves or surges in

the pipe.

suspended solids. I)Solids that either float on the surface or

are suspended in water or other liquids, and which are

largely removable by laboratory filtering. 2) The quantity of

material removed from water in a laboratory test, as



synergism. An interaction of two or more chemicals which

results in an effect that is greater than the sum of their

effects taken independently.

system with a single service connection. A system which

supplies drinking water to consumers via a single service


systemic. Relating to whole body, rather than its individual


systemic effects. Effects observed at sites distant from the

entry point of a chemical due to its absorption and distribu-

tion into the body.

sounding tube. A pipe or tube used for measuring the depths

of water.


TCE. See trichloroethane

TDS. See total dissolved solids.

telemetry (tel-LEM-uh-tree). The electrical link between

the transmitter and the receiver. Telephone lines are

commonly used to serve as the electrical line.

temperature sensor. A device that opens and closes a switch

in response to changes in the temperature. This device

might be a metal contact, or a thermocouple that generates

minute electrical current proportional to the difference in

heat, or a variable resistor whose value changes in response

to changes in temperature. Also called a heat sensor

teratogenesis. The induction of nonhereditary congenital

malformations (birth defects) in a developing fetus by

exogenous factors acting in the womb; interference with

normal embryonic development.

teratogenicity. The capacity of a physical or chemical agent

to cause teratogenesis in offspring.

terrace. A broad channel, bench, or embankment con-

structed across the slope to intercept runoff and detain or

channel it to protected outlets, thereby reducing erosion

from agricultural areas.

therapeutic index. The ratio of the dose required to produce

toxic or lethal effect to dose required to produce nonadverse

or therapeutic response.

thermal stratification (STRAT-uh-fuh-KAY-shun). The

formation of layers of different temperatures in a lake or

reservoir. Also see stratification

thermocline (THUR-moe-KLINE). The middle layer in a

thermally stratified lake or reservoir. In this layer there is a

rapid decrease in temperature with depth. Also called the


thermocouple. A heat-sensing device made of two conduc-

tors of different metals joined at their ends. An electric

current is produced when there is a difference in tempera-

ture between the ends.

THM See trihalomethanes

THM precursor. See precursor, THM.

threshold. The lowest dose of a chemical at which a speci-

fied measurable effect is observed and below which it is not


threshold odor. The minimum odor of a water sample that

can just be detected after successive dilutions with odorless

water. Also called odor threshold

threshold odor number. The greatest dilution of a sample

with odor-free water that still yields a just-detectable odor.

thrust block. A mass of concrete or similar material appro-

priately placed around a pipe to prevent movement when

the pipe is carrying water. Usually placed at bends and

valve structures.

tillage. Plowing, seedbed preparation, and cultivation


time lag. The time required for processes and control systems

to respond to a signal or to reach a desired level.

timer. A device for automatically starting or stopping a

machine or other device at a given time.

time-weighted average. The average value of a parameter

(e.g., concentration of a chemical in air) that varies over


tissue. A group of similar cells.

titrate (TIE-trate). To TITRATE a sample, a chemical

solution of known strength is added on a drop-by-drop basis

until a certain color change, precipitate, or pH change in the

sample is observed (end point). Titration is the process of

adding the chemical reagent in increments until completion

of the reaction, as signaled by the end point.

TNCWS. See transient non-community water system.

too numerous to count. The total number of bacterial

colonies exceeds 200 on a 47-nun diameter membrane filter

used for coliform detection.

topography. The arrangement of hills and valleys in a

geographic area.

total dissolved phosphorus. Total phosphorus content of

material that will pass through a filter of a specific size.

total dissolved solids (TDS). All of the dissolved solids in a

water. TDS is measured on a sample of water that has

passed through a very fine mesh filter to remove suspended

solids. The water passing through the filter is evaporated

and the residue represents the dissolved solids. Also see

specific conductance

total dynamic head (TDH). When a pump is lifting or

pumping water, the vertical distance (in feet) from the

elevation of the energy grade line on the suction side of the

pump to the elevation of the energy grade line on the

discharge side of the pump.

total nitrogen. The sum of all nitrogen forms.

total particulate phosphorus. Total phosphorus content of

material retained on a filter of a specific size.

total phosphorus. The sum of all phosphorus forms.

total residual chlorine. The amount of available chlorine

remaining after a given contact time. The sum of the

combined available residual chlorine and the free available

residual chlorine. Also see residual chlorine

total trihalomethanes (THMs). The sum of the concentra-

tion, in milligrams per liter, of the several trihalomethane

compounds, rounded to two significant figures.

total trihalomethanes (TTHM). The sum of the concentra-

tion in milligrams per liter of the trihalomethane com-

pounds (trichloromethane [chloroform],

dibromochloromethane, bromodichloromethane and

tribromomethane [bromoform]), rounded to two significant


totalizer. A device or meter that continuously measures and

calculates (adds) total flows in gallons, million gallons,

cubic feet, or some other unit of volume measurement. Also

called an integrator.

toxaphene (TOX-uh-FEEN). A chemical that causes

adverse health effects in domestic water supplies and also is

toxic to freshwater and marine aquatic life.

toxic (TOX-ick). A substance which is poisonous to an


toxic pollutants. Materials contaminating the environment

that cause death, disease. birth defects in organisms that

ingest or absorb them. The quantities and length of expo-

sure necessary to cause these effects can vary widely.

toxic substance. A chemical or mixture that may represent an

unreasonable risk of injury to health or the environment.

toxicant A harmful substance or agent that may injure an

exposed organism.

toxicity. The quality or degree of being poisonous or harmful

to plant, animal or human life.

toxicity assessment Characterization of the toxicological

properties and effects of a chemical, including all aspects of

its absorption, metabolism, excretion and mechanism of

action, with special emphasis on establishment of dose-

response characteristics.

toxicology. The science and study of poisons control.

transducer (trans-DUE-sir). A device which senses some

varying condition and converts it to an electrical signal for

transmission to some other device (a receiver) for process-

ing or decision making.

transformation. Acquisition by a cell of the property of

uncontrolled growth.

TWS. See transient water system.

transient water system. A non-community water system that

does not serve 25 of the same nonresident persons per day

for more than six months per year. Also called a transient

non-community water system (TNCWS).

transmission lines. Pipelines that transport raw water from

its source to a water treatment plant. After treatment, water

is usually pumped into pipelines (transmission lines) that

are connected to a distribution grid system.

transmissivity. The ability of an aquifer to transmit water.

transpiration (TRAN-spur-RAY-shun).The process by

which water vapor is released to the atmosphere by living


treated wastewater. Wastewater that has been subjected to

one or more physical, chemical, and biological processes to

reduce its pollution of health hazard.

tremie (TREH-me). A device used to place concrete or grout

under water.

trichloroethane (TCE) (try-KLOR-o-ETH-hane). An

organic chemical used as a cleaning solvent that causes

adverse health effects in domestic water supplies.

trihalomethane . One of a family of organic com-

pounds named as derivatives of methane. THMs are

generally the by-product from chlorination of drinking

water that contains organic material. The resulting com-

pounds (THMs) are suspected of causing cancer.

tube settler. A device that uses bundles of small bore (2 to 3

inches or 50 to 75 mm) tubes installed on an incline as an

aid to sedimentation. The tubes may come in a variety of

shapes including circular and rectangular. As water rises

within the tubes, settling solids fall to the tube surface. As

the sludge (from the settled solids) in the tube gains weight,

it moves down the tubes and settles to the bottom of the

basin for removal by conventional sludge collection means.

Tube settlers are sometimes installed in sedimentation

basins and clarifiers to improve particle removal.

tubercle (TOO-burr-cull). A protective crust of corrosion

products (rust) which builds up over a pit caused by the loss

of metal due to corrosion.

tuberculation (too-BURR-que-LAY-shun). The develop-

ment or formation of small mounds of corrosion products

(rust) on the inside of iron pipe. These mounds (tubercules)

increase the roughness of the inside of the pipe thus

increasing resistance to water flow.

turbid. Having a cloudy or muddy appearance.

turbidimeter. A device that measures the amount of sus-

pended solids in a liquid.

turbidity (ter-BID-it-tee). The cloudy appearance of water

caused by the presence of suspended and colloidal matter.

In the waterworks field, a turbidity measurement is used to

indicate the clarity of water. Technically, turbidity is an

optical property of the water based on the amount of light

reflected by suspended particles. Turbidity cannot be

directly equated to suspended solids because white particles

reflect more light than dark-colored particles and many

small particles will reflect more light than an equivalent

large particle.


uncertainty factor. A number (equal to or greater than one)

used to divide NOAEL or LOAEL values derived from

measurements in animals or small groups of humans, in

order to estimate a NOAEL value for the whole human


unconfined aquifer. An aquifer containing water that is not

under pressure; the water level in a well is the same as the

water table outside the well.

unit cancer risk. Estimate of the lifetime risk caused by each

unit of exposure in the low exposure region.

unit hydrograph. The hydrograph of one inch of storm

runoff generated by a rainstorm of fairly uniform intensity

within a specific period of time.

unsaturated zone. The area between the land surface and

water table in which the pore spaces are only partially filled

with water. Also called "zone of aeration".

upper-bound estimate. Estimate not likely to be lower than

the true risk.

urban runoff. Stormwater from city streets and adjacent

domestic or commercial properties that may carry pollutants

of various kinds into the sewer systems and/or receiving


user fee. A fee which is collected only from those persons

who use a particular service, as opposed to one collected

from the public in general. User fees generally vary in

proportion to the degree of use of the service.

UST'S. Underground storage tanks.


variable costs. Input costs that change as the nature of the

production activity of its circumstances change; for ex-

ample, as production levels vary.

variance. A State with primacy may relieve a public water

system from a requirement respecting an MCL by granting

a variance if certain conditions exist. These are: 1) the

system cannot meet the MCL in spite of the application of

best available treatment technology, treatment techniques or

other means (taking costs into consideration), due to the

characteristics of the raw water sources which are reason-

ably available to the system, and 2) the variance will not

result in an unreasonable public health risk. A system may

also be granted a variance from a specified treatment

technique if it can show that, due to the nature of the

system's raw water source, such treatment is not necessary

to public health. Also see exemption.

vegetative controls. Non-point source pollution control

practices that involve plants (vegetative cover) to reduce

erosion and minimize the loss of pollutants.

virus. The smallest form of microorganisms capable of

causing disease. Especially, a virus of fecal origin that is

infectious to humans by waterborne transmission.

volatile. Readily vaporizable at a relatively low temperature.

volatile acids. Acids produced during digestion. Fatty acids

which are soluble in water and can be steam-distilled at

atmospheric pressure. Also called "organic acids." Volatile

acids are commonly reported as equivalent to acetic acid.

volatile liquids. Liquids which easily vaporize or evaporate

at room temperatures.

volatile solids. Those solids in water or other liquids that are

lost on ignition of the dry solids at 550 degrees C.

volatilization. Loss of a substance through evaporation.

voltage. The electrical pressure available to cause a flow of

current (amperage) when an electrical circuit is closed. See

electromotive force (E.M.F.).

volumetric. A measurement based on the volume of some

factor. Volumetric titration is a means of measuring

unknown concentrations of water quality indicators in a

sample by determining the volume of titrant or liquid

reagent needed to complete particular reactions.

vortex. A revolving mass of water which forms a whirlpool.

This whirlpool is caused by water flowing out of a small

opening in the bottom of a basin or reservoir. A funnel-

shaped opening is created downward from the water



wastewater. The used water and solids from a community

(including used water from industrial processes) that flow to

a treatment plant. Storm water, surface water, and ground-

water infiltration also may be included in the wastewater

that enters a wastewater treatment plant. The term -sewage

usually refers to household wastes, but this word is being

replaced by the term -wastewater.

wastewater treatment plant. A facility that receives

wastewaters ( and sometimes runoff) from domestic and/or

industrial sources, and by a combination of physical,

chemical, and biological processes reduces (treats) the

wastewaters to less harmful byproducts; known by the

acronyms , STP (sewage treatment plant), and

POTW (publicly owned treatment works).

waterborne disease outbreak. The significant occurrence of

acute infectious illness, epidemiologically associated with

the ingestion of water from a public water system that is

deficient in treatment, as determined by the appropriate

local or state agency

water budget. A summation of inputs, outputs, and net

changes to a particular water resource system over a fixed

period. (Also, water balance model).

water hammer. The sound like someone hammering on a

pipe that occurs when a valve is opened or closed very

rapidly. When a valve position is changed quickly, the

water pressure in a pipe will increase and decrease back and

forth very quickly. This rise and fall in pressures can do

serious damage to the system.

water purveyor (purr-VAY-or). An agency or person that

supplies water (usually potable water).

water solubility. The maximum concentration of a chemical

compound which can result when it is dissolved in water. If

a substance is water soluble, it can very readily disperse

through the environment.

water storage pond. An impound for liquid wastes, so

designated as to accomplish some degree of biochemical

treatment of the wastes.

water supplier. A person who owns or operates a public

water system.

water supply system. The collection, treatment, storage, and.

distribution of potable water from source to consumer.

water table. The level of ground water. The upper surface of

the zone of saturation of groundwater above an imperme-

able layer of soil or rock (through which water cannot

move) as in an unconfined aquifer. This level can be very

near the surface of the ground or far below it.

water treatment lagoon. An impound for liquid wastes, so

designed as to accomplish some degree of biochemical

treatment of the wastes.

water well. An excavation where the intended use is for the

location, acquisition, development, or artificial recharge of

groundwater (excluding Sandpoint wells).

watershed. The land area that drains into a stream. An area

of land that contributes runoff to one specific delivery point;

large watersheds may be composed of several smaller

"subsheds", each of which contributes runoff to different

locations that ultimately combine at a common delivery


watt A unit of power equal to one joule per second. The

power of a current of one ampere flowing across a potential

difference of one volt.

weir (weer). 1) A wall or plate placed in an open channel and

used to measure the flow of water. The depth of the flow

over the weir can be used to calculate the flow rate, or a

chart or conversion table may be used. 2) A wall or obstruc-

tion used to control flow (from settling tanks and clarifiers)

to assure uniform flow rate and avoid short-circuiting.

weir diameter (weer). Many circular clarifiers have a

circular weir within the outside edge of the clarifier. All the

water leaving the clarifier flows over this weir. The

diameter of the weir is the length of a line from one edge of

a weir to the opposite edge and passing through the center

of the circle formed by the weir

weir loading. A guideline used to determine the length of

weir needed on settling tanks and clarifiers in treatment

plants. Used by operators to determine if weirs are hydrauli-

cally (flow) overloaded.

Weir Loading (GPM/ft) = Flow (GPM)/ Length of Weir (ft)

well. A bored, drilled, or driven shaft, or a dug hole, whose

depth is greater than the largest surface dimension and

whose purpose is to reach underground water supplies or

oil, or to store or bury fluids below ground.

well field. Area containing one or more wells that produces

usable amount of water.

well monitoring. The measurement, by on-site instruments or

laboratory methods, of the quality of water in a well.

well plug. A watertight and gastight seal installed in a bore

hole or well to prevent movement of fluids.

wet chemistry. Laboratory procedures used to analyze a

sample of water using liquid chemical solutions (wet)

instead of, or in addition to, laboratory instruments.

wetlands. Any number of tidal and nontidal areas character-

ized by saturated or nearly saturated soils most of the year

that form an interface between terrestrial (land-based) and

aquatic environments; include freshwater marshes around

ponds and channels (rivers and streams), brackish and salt

marshes; other common names include swamps and bogs.

wire-to-water efficiency. The efficiency of a pump and

motor together. Also called the overall efficiency.

withdrawal The process of taking water from a source and

conveying it to a place for a particular type of use.


yield. The quantity of water (expressed as a rate of flow-

GPM, GPH, GPD, or total quantity per year) that can be

collected for a given use from surface or groundwater

sources. The yield may vary with the use proposed, with the

plan of development, and also with economic consider-

ations. Also see safe yield.


zeta potential. In coagulation and flocculation procedures,

the difference in the electrical charge between the dense

layer of ions surrounding the particle and the charge of the

bulk of the suspended fluid surrounding this particle. The

zeta potential is usually measured in millivolts.

zone of aeration. The comparatively dry soil or rock located

between the ground surface and the top of the water table.

zone of saturation. The soil or rock located below the top of

the groundwater table. By definition, the zone of saturation

is saturated with water. Also see water table.

zooplankton (ZOE-PLANK-ton). Small, usually micro-

scopic animals(such as protozoans), found in lakes and