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Drinking Water Glossary

Office Of Water

Drinking Water Glossary

A Dictionary of Technical and Legal Terms Related to Drinking Water

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E

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 grains.
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 chemical 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 electrolytic 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 application 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 substances or waste. The endangerment assessment document is prepared in support of enforcement actions under CERCLA or RCRA.
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 bacteria.
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 variance.
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 quantifying exposure in a given situation.
extrapolation. Estimation of unknown values by extending or projecting from known values.

F

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 pathogens.
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 consumers. 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 chemicals 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 irregularities. 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 floods.
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 filter.
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 teeth.
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, relatively 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 EXPANSION
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 restrictions 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.

G

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 decomposition 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 SERIES.
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, magnesium, 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 administered 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 pollutants 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.

H

half-life. The length of time required for the mass, concentration, or activity of a chemical or physical agent to be reduced by one-half.
halogen. One of the chemical elements chlorine, bromine, or iodine.
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 sometimes 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 SENSOR.
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; hemopoiesis.
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 manmade 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 microorganisms 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 connected.
HTH (pronounce as separate letters). High Test Hypochlorite. 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 assessment 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 exposures.
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 rock.
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.

I

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 water.
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 indicator 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 openjointed 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 compliance period which begins at least 18 months after promulgation.
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 environment.
instream uses. Water uses that can be carried out without removing the water from its source, as in navigation and recreation.
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 substances 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 soil.
interlock An electrical switch, usually magnetically operated. 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 electrons.
ionic concentration. The concentration of any ion in solution, 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 agent.

J

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 coagulant 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 motor.
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.

K

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.

L

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 protection 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 contaminants 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 recharge.
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 metals.
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 line.
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 instrument.
linearized multistage model. Derivation of the multistage model, where the data are assumed to be linear at low doses.
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 environment (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."

M

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 radionuclides 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 uranium-238.
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 life.
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 (anabolism).
metabolite. Any product of metabolism, especially a transformed 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 THERMOCLINE.
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 - trichloroethane.
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 alkalinity is expressed as milligrams per liter equivalent calcium carbonate.
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 example, 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 tissues.
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 percent.
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 carcinogenicity.
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 recombination.
mutagenicity. The capacity of a chemical or physical agent to cause permanent alteration of the genetic material within living cells.

N

N. See normal.
National Environmental Training Association (NETA). A professional organization devoted to serving the environmental trainer and promoting better operation of waterworks 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 NIOSH.
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. Commonly 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 Regulations.
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 compounds.
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 nutrients.
nutrient pollution. Contamination of water resources by excessive inputs of nutrients; insurface waters, excess algal production is a major concern.

References

Water Treatment Plant Operation. California State University, Sacramento, School of Engineering, Applied Research and Design Center. 1988. Surface Water Treatment: The New Rules. Harry von Huben. American Water Works Association. 1991. Safe Drinking Water Act Amendments, Regulations and Standards. Calabrese, EJ; Gilbert, CE and Pastides, H. Eds. Lewis Publishers. Chelsea Michigan. 1988. Water Resources Planning. Dzurik, AA. Rowman & Littlefield, Savage, MD. 1990. Code of Federal Regulations, Title 40, Chapter I, Section 141.2.July 1, 1991 Federal Register 56 FR 26547, June 7, 1991 (Lead and Copper) 56 FR 3578, January 30, 1991 (Phase 11)

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