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Skip Navigation LinksWaterRF Home > Resources > Glossary
WaterRF Home > Resources > Glossary
 

Acronyms. Industry jargon. Scientific terminology.

Our glossary makes information easy to find and understand.

Note:  Most of the terms and definitions were obtained from http://www.epa.gov/

Expand (+) the letters below to see terms and definitions.

 Glossary
TermDefinition
expand  A
Absorption
The uptake of water , other fluids, or dissolved chemicals by a cell or an organism (as tree roots absorb dissolved nutrients in soil.)
Acid Rain
Precipitation which has been rendered (made) acidic by airborne pollutants.
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.
ACWA
Association of California Water Agencies
Aeration
A process which promotes biological degradation of organic matter in water. The process may be passive (as when waste is exposed to air), or active (as when a mixing or bubbling device introduces the air).
AGA
American Gas Association
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 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.
Algae
Simple rootless plants that grow in sunlit waters in proportion to the amount of available nutrients. They can affect water quality adversely by lowering the dissolved oxygen in the water. They are food for fish and small aquatic animals.
Algicide
Substance or chemical used specifically to kill or control algae.
Alkaline
The condition of water or soil which contains a sufficient amount of alkali substance to raise the pH above 7.0
Alluvial
Relating to and/or sand deposited by flowing water
Ambient
Environmental or surrounding conditions.
AMWA
Association of Metropolitan Water Agencies
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 instrumentation.
Anti-Microbial
An agent that kills microbes.
Appurtenance
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.
Aquifer
An underground geological formation, or group of formations, containing water. Are sources of groundwater for wells and springs.
Aquitard
Geological formation that may contain groundwater but is not capable of transmitting significant quantities of it under normal hydraulic gradients. May function as confining bed.
Arsenic
A semi-metal element that enters drinking water supplies from natural deposits in the earth or from agricultural and industrial practices.  Has been linked to numerous non-cancer health effects and cancer of the bladder, lungs, skin, kidney, nasal passages, liver, and prostate.  USEPA has set the arsenic standard for drinking water at 10 parts per billion for consumers served by public water systems as of January 23, 2006.
ASCE
American Society of Civil Engineers
Assay
A test for a specific chemical, microbe, or effect.
Assimilation
The ability of a body of water to purify itself of pollutants.
Association of Boards of Certification
An international organization representing boards which certify the operators of waterworks and wastewater facilities.
Available Chlorine
A measure of the amount of chlorine available in chlorinated lime, hypochlorite compounds, and other materials used as a source of chlorine when compared with that of liquid or gaseous chlorines.
AWWA
American Water Works Association
expand  B
Back Pressure
A pressure that can cause water to backflow into the water supply when a user's waste water system is at a higher pressure than the public system.
Backwashing
Reversing the flow of water back through the filter media to remove entrapped solids.
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 solutions, slurry).
Bench-Scale Tests
Laboratory testing of potential cleanup technologies
Best Available Technology (BAT)
The best technology treatment techniques, or other means which the Administrator finds, after examination for efficacy under field conditions 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.
Bioassay
A test to determine the relative strength of a substance by comparing its effect on a test organism with that of a standard preparation.
Bioremediation
A process of adding nutrient to ground water to speed up the natural process in which bacteria break down gasoline into harmless compounds.
Bloom
A proliferation of algae and/or higher aquatic plants in a body of water; often related to pollution, especially when pollutants accelerate growth.
Breakpoint Chlorination
Addition of chlorine to water until the chlorine demand has been satisfied.
Buffer
A solution or liquid whose chemical makeup neutralizes acids or bases without a great change in pH.
By-product
Material, other than the principal product, generated as a consequence of an industrial process or as a breakdown product in a living system.
expand  C
Caisson
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 water.
Capillary Action
The movement of water through very small spaces due to molecular forces.
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.
Case Study
A brief fact sheet providing risk, cost, and performance information on alternative methods and other pollution prevention ideas, compliance initiatives, voluntary efforts, etc.
Cathode
The negative pole or electrode of an electrolytic cell or system. The cathode attracts positively charged particles or ions (cations).
Cation
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.
Cavitation
The formation and collapse of gas pockets or bubbles on the blade of an impeller or the gate of a valve; collapse of these pockets or bubbles drives water with such force that it can cause pitting of the gate or valve surface.
Centrate
The water leaving a centrifugal after most of the solids have been removed.
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 direction of normal flow.
Chemical Treatment
Any one of a variety of technologies that use chemicals or a variety of chemical processes to treat waste.
Chlorinated Hydrocarbons
1. Chemicals containing only chlorine, carbon, and hydrogen. These include a class of persistent, broad-spectrum insecticides that linger in the environment and accumulate in the food chain. Among them are DDT, aldrin, dieldrin, heptachlor, chlordane, lindane, endrin, Mirex, hexachloride, and toxaphene. Other examples include TCE, used as an industrial solvent. 2. Any chlorinated organic compounds including chlorinated solvents such as dichloromethane, trichloromethylene, chloroform.
Chlorination
The application of chlorine to drinking water, sewage, or industrial waste to disinfect or to oxidize undesirable compounds.
Chlorine
Water additive used to control microbes.
 
Chlorophenoxy
A class of herbicides that may be found in domestic water supplies and cause adverse health effects.
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.
Class (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.
Climate Change
The term 'climate change' is sometimes used to refer to all forms of climatic inconsistency, but because the Earth's climate is never static, the term is more properly used to imply a significant change from one climatic condition to another. In some cases, 'climate change' has been used synonymously with the term, 'global warming'; scientists however, tend to use the term in the wider sense to also include natural changes in climate.
Coagulation
Clumping of particles in wastewater to settle out impurities, often induced by chemicals such as lime, alum, and iron salts.
Coliform Index
A rating of the purity of water based on a count of fecal bacteria.
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 concentrations of the chemical.
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.
Complete Treatment
A method of treating water that consists of the addition of coagulant chemicals, flash mixing, coagulation-flocculation, sedimentation, and filtration. Also called conventional filtration.
Compliance Monitoring
Collection and evaluation of data, including self-monitoring reports, and verification to show whether pollutant concentrations and loads contained in permitted discharges are in compliance with the limits and conditions specified in the permit.
Condition Assessment
Encompasses the collection of data and information through direct inspection, observation and investigation, in-direct monitoring and reporting, and the analysis of the data and information to make a determination of the structural, operational, and performance status of capital infrastructure assets. Also includes the practice of failure analysis which seeks to determine the causes of infrastructure failures in order to prevent future failures.
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 influence.
Confined Aquifer
An aquifer in which ground water is confined under pressure which is significantly greater than atmospheric pressure.
Constituent(s) of Concern
Specific chemicals that are identified for evaluation in the site assessment process
Contaminant
Any physical, chemical, biological, or radiological substance or matter that has an adverse effect on air, water, or soil.
Continuous Discharge
A routine release to the environment that occurs without interruption, except for infrequent shutdowns for maintenance, process changes, etc.
Control System
A system which senses and controls its own operation on a close, continuous basis in what is called proportional (or modulating) control.
Conventional Filtration Treatment
A series of processes including coagulation, flocculation, sedimentation, and filtration resulting in substantial particulate removal.
Corrosion
The dissolution and wearing away of metal caused by a chemical reaction such as between water and the pipes, chemicals touching a metal surface, or contact between two metals.
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/Benefit Analysis
A quantitative evaluation of the costs which would have incurred by implementing an environmental regulation versus the overall benefits to society of the proposed action.
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
Cross Contamination
The movement of underground contaminants from one level or area to another due to invasive subsurface activities.
Cryptosporidium
A protozoan microbe associated with the disease cryptosporidiosis in man. The disease can be transmitted through ingestion of drinking water, person-to-person contact, or other pathways, and can cause acute diarrhea, abdominal pain, vomiting, fever, and can be fatal
CUWA
California Urban Water Agencies
expand  D
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 AGE TANK.
Dechlorination
Removal of chlorine from a substance.
Decontamination
Removal of harmful substances such as noxious chemicals, harmful bacteria or other organisms, or radioactive material from exposed individuals, rooms and furnishings in buildings, or the exterior environment.
Defluoridation
The removal of excess flouride in drinking water to prevent the staining of teeth.
Demineralization
A treatment process that removes dissolved minerals from water.
Dense Non-Aqueous Phase Liquid (DNAPL)
Non-aqueous phase liquids such as chlorinated hydrocarbon solvents or petroleum fractions with a specific gravity greater than 1.0 that sink through the water column until they reach a confining layer. Because they are at the bottom of aquifers instead of floating on the water table, typical monitoring wells do not indicate their presence.
Desalination
(1) Removing salts from ocean or brackish water by using various technologies. (2) Removal of salts from soil by artificial means, usually leaching.
Designated Uses
Those water uses identified in state water quality standards that must be achieved and maintained as required under the Clean Water Act. Uses can include cold water fisheries, public water supply, and irrigation.
Detectable Leak Rate
The smallest leak (from a storage tank), expressed in terms of gallons- or liters-per-hour, that a test can reliably discern with a certain probability of detection or false alarm.
Detection Limit
The lowest concentration of a chemical that can reliably be distinguished from a zero concentration.
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.
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.
Dimictic
Lakes and reservoirs that freeze over and normally go through two stratifications and two mixing cycles a year.
Direct Runoff
Water that flows over the ground surface or through the ground directly into streams, rivers, and lakes.
Disinfectant Time
The time it takes water to move from the point of disinfectant application (or the previous point of residual disinfectant measurement) to a point before or at the point where the residual disinfectant is measured. In pipelines, the time is calculated by dividing the internal volume of the pipe by he maximum hourly flow rate; within mixing basins and storage reservoirs it is determined by tracer studies of an equivalent demonstration.
Disinfection By-Product
A compound formed by the reaction of a disinfectant such as chlorine with organic material in the water supply.
Dissolved Solids
Disintegrated organic and inorganic material in water. Excessive amounts make water unfit to drink or use in industrial processes.
Diversion
1. Use of part of a stream flow as water supply. 2. A channel with a supporting ridge on the lower side constructed across a slope to divert water at a non-erosive velocity to sites where it can be used and disposed of.
Dose Rate
In exposure assessment, dose per time unit (e.g. mg/day), sometimes also called dosage.
Dose Response Curve
Graphical representation of the relationship between the dose of a stressor and the biological response thereto.
Dose-Response Relationship
The quantitative relationship between the amount of exposure to a substance and the extent of toxic injury or disease produced.
Downgradient
The direction that groundwater flows; similar to "downstream" for surface water.
Drainage
Improving the productivity of agricultural land by removing excess water from the soil by such means as ditches or subsurface drainage tiles.
Drainage Well
A well drilled to carry excess water off agricultural fields. Because they act as a funnel from the surface to the groundwater below. Drainage wells can contribute to groundwater pollution.
Drinking Water Equivalent Level
Protective level of exposure related to potentially non-carcinogenic effects of chemicals that are also known to cause cancer.
Drive Point Profiler
An exposed groundwater DP system used to collect multiple depth-discrete groundwater samples. Ports in the tip of the probe connect to an internal stainless steel or teflon tube that extends to the surface. Samples are collected via suction or airlift methods. Deionized water is pumped down through the ports to prevent plugging while driving the tool to the next sampling depth.
expand  E
EAWAG
Swiss Federal Institute for Environmental Science and Technology
EDCs
Endocrine Disrupting Compounds/Chemicals. Exogenous agents that interfere with the synthesis, secretion, transport, binding, action, or elimination of natural hormones in the body that are responsible for the maintenance of homeostasis, reproduction, development, and/or behavior.
Effluent Guidelines
Technical EPA documents which set effluent limitations for given industries and pollutants.
Ejector
A device used to disperse a chemical solution into water being treated.
Electrodialysis
A process that uses electrical current applied to permeable membranes to remove minerals from water. Often used to desalinize salty or brackish water.
Endrin
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.
Enforceable Requirements
Conditions or limitations in permits issued under the Clean Water Act Section 402 or 404 that, if violated, could result in the issuance of a compliance order or initiation of a civil or criminal action under federal or applicable state laws. If a permit has not been issued, the term includes any requirement which, in the Regional Administrator's judgment, would be included in the permit when issued. Where no permit applies, the term includes any requirement which the RA determines is necessary for the best practical waste treatment technology to meet applicable criteria.
Enrichment
The addition of nutrients (e.g. nitrogen, phosphorus, carbon compounds) from sewage effluent or agricultural runoff to surface water, greatly increases the growth potential for algae and other aquatic plants.
Environment
The sum of all external conditions affecting the life, development and survival of an organism.
Environmental Impact Statement
A document required of federal agencies by the National Environmental Policy Act for major projects or legislative proposals significantly affecting the environment. A tool for decision making, it describes the positive and negative effects of the undertaking and cites alternative actions.
Environmental Sustainability
Long-term maintenance of ecosystem components and functions for future generations.
Enzymes
Organic substances (produced by living organisms) which cause or speed up chemical reactions. Organic catalysts and/or biochemical catalysts.
Episode (Pollution)
An air pollution incident in a given area caused by a concentration of atmospheric pollutants under meteorological conditions that may result in a significant increase in illnesses or deaths. May also describe water pollution events or hazardous material spills.
EPRI CEC
Electric Power Research Institute Community Environmental Center
Established Treatment Technologies
Technologies for which cost and performance data are readily available.
Eutrophic Lakes
Shallow, murky bodies of water with concentrations of plant nutrients causing excessive production of algae.
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
Exempted Aquifer
Underground bodies of water defined in the Underground Injection Control program as aquifers that are potential sources of drinking water though not being used as such, and thus exempted from regulations barring underground injection activities.
Exotic Species
A species that is not indigenous to a region.
Exposure Assessment
Identifying the pathways by which toxicants may reach individuals, estimating how much of a chemical an individual is likely to be exposed to, and estimating the number likely to be exposed.
Exposure Indicator
A characteristic of the environment measured to provide evidence of the occurrence or magnitude of a response indicator's exposure to a chemical or biological stress.
Exposure Pathway
The path from sources of pollutants via, soil, water, or food to man and other species or settings.
Extraction Well
A discharge well used to remove groundwater or air.
expand  F
Facilities Plans
Plans and studies related to the construction of treatment works necessary to comply with the Clean Water Act or RCRA. A facilities plan investigates needs and provides information on the cost-effectiveness of alternatives, a recommended plan, an environmental assessment of the recommendations, and descriptions of the treatment works, costs, and a completion schedule.
Fecal Coliform Bacteria
Bacteria found in the intestinal tracts of mammals. Their presence in water or sludge is an indicator of pollution and possible contamination by pathogens.
Ferrous Metals
Magnetic metals derived from iron or steel; products made from ferrous metals include appliances, furniture, containers, and packaging like steel drums and barrels. Recycled products include processing tin/steel cans, strapping, and metals from appliances into new products.
Finished Water
Water is "finished" when it has passed through all the processes in a water treatment plant and is ready to be delivered to consumers.
Fix a Sample
A sample is "fixed" in the field by adding chemicals that prevent water quality indicators of interest in the sample from changing before laboratory measurements are made.
Flocculation
Process by which clumps of solids in water or sewage aggregate through biological or chemical action so they can be separated from water or sewage.
Flow Rate
The rate, expressed in gallons -or liters-per-hour, at which a fluid escapes from a hole or fissure in a tank. Such measurements are also made of liquid waste, effluent, and surface water movement.
Fluidized
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
The addition of a chemical to increase the concentration of fluoride ions in drinking water to reduce the incidence of tooth decay.
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.
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.
Fresh Water
Water that generally contains less than 1,000 milligrams-per-liter of dissolved solids.
expand  G
GAC
Granular Activated Carbon. A filtering system often used in small water systems and individual homes to remove organics. Also used by municipal water treatment plants. GAC can be highly effective at lowering elevated levels of radon in water.
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.
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.
Genotoxic
Damaging to DNA; pertaining to agents known to damage DNA.
Germicide
A substance formulated to kill germs or microorganisms. The germicidal properties of chlorine make it an effective disinfectant.
GITA
Geospatial Information and Technology Association
Global Warming
An increase in the near surface temperature of the Earth. Global warming has occurred in the distant past as the result of natural influences, but the term is most often used to refer to the warming predicted to occur as a result of increased emissions of greenhouse gases. Scientists generally agree that the Earth's surface has warmed by about 1 degree Fahrenheit in the past 140 years. The Intergovernmental Panel on Climate Change (IPCC) recently concluded that increased concentrations of greenhouse gases are causing an increase in the Earth's surface temperature and that increased concentrations of sulfate aerosols have led to relative cooling in some regions, generally over and downwind of heavily industrialized areas.
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.
Granular Activated Carbon Treatment
A filtering system often used in small water systems and individual homes to remove organics. Also used by municipal water treatment plants. GAC can be highly effective in lowering elevated levels of radon in water.
Gray Water
Domestic wastewater composed of wash water from kitchen, bathroom, and laundry sinks, tubs, and washers.
Greenhouse Gas
A gas, such as carbon dioxide or methane, which contributes to potential climate change.
Groundwater Discharge
Ground water entering near coastal waters which has been contaminated by landfill leachate, deep well injection of hazardous wastes, septic tanks, etc.
Groundwater Under the Direct Influence (UDI) of Surface Water
Any water beneath the surface of the ground with: 1. significant occurrence of insects or other microorganisms, algae, or large-diameter pathogens; 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 is determined for individual sources in accordance with criteria established by a state.
GWRC
Global Water Research Coalition
expand  H
Hazardous Substance
1. Any material that poses a threat to human health and/or the environment. Typical hazardous substances are toxic, corrosive, ignitable, explosive, or chemically reactive. 2. Any substance designated by EPA to be reported if a designated quantity of the substance is spilled in the waters of the United States or is otherwise released into the environment.
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.
Health Advisory Level
A non-regulatory health-based reference level of chemical traces (usually in ppm) in drinking water at which there are no adverse health risks when ingested over various periods of time. Such levels are established for one day, 10 days, long-term and life-time exposure periods. They contain a wide margin of safety.
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 risk to humans and animals from the measured high-exposure-high-risk data involving laboratory animals.
Hose Bib
Faucet. A location in a water line where a hose is connected.
Human Health Risk
The likelihood that a given exposure or series of exposures may have damaged or will damage the health of individuals.
Hydraulic Conductivity
The rate at which water can move through a permeable medium. (i.e. the coefficient of permeability.)
Hydrocarbons (HC)
Chemical compounds that consist entirely of carbon and hydrogen.
Hydrogeological Cycle
The natural process recycling water from the atmosphere down to (and through) the earth and back to the atmosphere again.
Hydrologic Cycle
Movement or exchange of water between the atmosphere and earth.
Hydrolysis
The decomposition of organic compounds by interaction with water.
Hydrophobic
Having a strong aversion for water.
Hydrostatic pressure
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.
Hypolimnion
Bottom waters of a thermally stratified lake. The hypolimnion of a eutrophic lake is usually low or lacking in oxygen.
expand  I
ILSI
International Life Sciences Institute
Imminent Threat
A high probability that exposure is occurring.
Impermeable
Not easily penetrated. The property of a material or soil that does not allow, or allows only with great difficulty, the movement or passage of water.
in situ
In place, the original location, in the natural environment.
in vivo
With in a living organism; a laboratory experiment performed in which the substance under study is inserted into a living organism.
Infectious Agent
Any organism, such as a pathogenic virus, parasite, or bacterium, that is capable of invading body tissues, multiplying, and causing disease.
Infiltration Gallery
A sub-surface groundwater collection system, typically shallow in depth, constructed with open-jointed or perforated pipes that discharge collected water into a watertight chamber from which the water is pumped to treatment facilities and into the distribution system. Usually located close to streams or ponds.
Inflow
Entry of extraneous rain water into a sewer system from sources other than infiltration, such as basement drains, manholes, storm drains, and street washing.
Initial Compliance Period (Water)
The first full three-year compliance period which begins at least 18 months after promulgation.
Innovative Treatment Technologies
Technologies whose routine use is inhibited by lack of data on performance and cost.
Inorganic Contaminants
Mineral-based compounds such as metals, nitrates, and asbestos. These contaminants are naturally-occurring in some water, but can also get into water through farming, chemical manufacturing, and other human activities. EPA has set legal limits on 15 inorganic contaminants.  
In-Situ Oxidation
Technology that oxidizes contaminants dissolved in ground water, converting them into insoluble compounds.
Instream Use
Water use taking place within a stream channel; e.g., hydro-electric power generation, navigation, water quality improvement, fish propagation, recreation.
Interface
The common boundary between two substances such as a water and a solid, water and a gas, or two liquids such as water and oil.
Internal Dose
In exposure assessment, the amount of a substance penetrating the absorption barriers (e.g. skin, lung tissue, gastrointestinal tract) of an organism through either physical or biological processes.
Interstitial Monitoring
The continuous surveillance of the space between the walls of an underground storage tank.
IOA
International Ozone Association
Ion Exchange Treatment
A common water-softening method often found on a large scale at water purification plants that remove some organics and radium by adding calcium oxide or calcium hydroxide to increase the pH to a level where the metals will precipitate out.
Irrigation
Applying water or wastewater to land areas to supply the water and nutrient needs of plants.
Isotropy
The condition in which the hydraulic or other properties of an aquifer are the same in all directions.
IWAP
International Water Association Publishing
expand  J
JWWA
Japan Water Works Association
expand  K
Kinetic Energy
Energy possessed by a moving object or water body.
Kiwa
Research institute in the Netherlands
expand  L
Lagoon
1. A shallow pond where sunlight, bacterial action, and oxygen work to purify wastewater; also used for storage of wastewater or spent nuclear fuel rods. 2. Shallow body of water, often separated from the sea by coral reefs or sandbars.
Large Water System
A water system that services more than 50,000 customers.
Latency
Time from the first exposure of a chemical until the appearance of a toxic effect.
Leachate Collection System
A system that gathers leachate and pumps it to the surface for treatment.
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.
Lead Service Line
A service line made of lead which connects the water to the building inlet and any lead fitting connected to it.
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).
Limnology
The study of the physical, chemical, hydrological, and biological aspects of fresh water bodies.
Liner
1. A relatively impermeable barrier designed to keep leachate inside a landfill. Liner materials include plastic and dense clay. 2. An insert or sleeve for sewer pipes to prevent leakage or infiltration.
Littoral Zone
1. That portion of a body of fresh water extending from the shoreline lakeward to the limit of occupancy of rooted plants. 2. A strip of land along the shoreline between the high and low water levels.
Lowest Acceptable Daily Dose
The largest quantity of a chemical that will not cause a toxic effect, as determined by animal studies.
expand  M
M/DBP Council
Microbial/Disinfectant By-products Research Council (Water Research Foundation, USEPA, and other parties to the regulation–negotiation process)
Manometer
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.
Maximum Contaminant Level Goal (MCLG)
Under the Safe Drinking Water Act, a non-enforceable concentration of a drinking water contaminant, set at the level at which no known or anticipated adverse effects on human health occur and which allows an adequate safety margin. The MCLG is usually the starting point for determining the regulated Maximum Contaminant Level.
Mechanical Aeration
Use of mechanical energy to inject air into water to cause a waste stream to absorb oxygen.
Media
Specific environments--air, water, soil--which are the subject of regulatory concern and activities.
Medium-size Water System
A water system that serves 3,300 to 50,000 customers.
Mesotrophic
Reservoirs and lakes which contain moderate quantities of nutrients and are moderately productive in terms of aquatic animal and plant life.
Methoxychlor
Pesticide that causes adverse health effects in domestic water supplies and is toxic to freshwater and marine aquatic life.
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.
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).
Mining of an Aquifer
Withdrawal over a period of time of ground water that exceeds the rate of recharge of the aquifer.
Mitigation
Measures taken to reduce adverse impacts on the environment.
Molecule
The smallest division of a compound that still retains or exhibits all the properties of the substance.
Monitoring Well
1. A well used to obtain water quality samples or measure groundwater levels. 2. A well drilled at a hazardous waste management facility or Superfund site to collect ground-water samples for the purpose of physical, chemical, or biological analysis to determine the amounts, types, and distribution of contaminants in the groundwater beneath the site.
Mudballs
Round material that forms in filters and gradually increases in size when not removed by backwashing.
Municipal Discharge
Discharge of effluent from waste water treatment plants which receive waste water from households, commercial establishments, and industries in the coastal drainage basin. Combined sewer/separate storm overflows are included in this category.
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National Estuary Program
A program established under the Clean Water Act Amendments of 1987 to develop and implement conservation and management plans for protecting estuaries and restoring and maintaining their chemical, physical, and biological integrity, as well as controlling point and nonpoint pollution sources.
National Pollutant Discharge Elimination System (NPDES)
A provision of the Clean Water Act which prohibits discharge of pollutants into waters of the United States unless a special permit is issued by EPA, a state, or, where delegated, a tribal government on an Indian reservation.
NCAR
National Center for Atmospheric Research
Neutralization
Decreasing the acidity or alkalinity of a substance by adding alkaline or acidic materials, respectively.
Nitrate
A compound containing nitrogen that can exist in the atmosphere or as a dissolved gas in water and which can have harmful effects on humans and animals. Nitrates in water can cause severe illness in infants and domestic animals. A plant nutrient and inorganic fertilizer, nitrate is found in septic systems, animal feed lots, agricultural fertilizers, manure, industrial waste waters, sanitary landfills, and garbage dumps
Nitrite
1. An intermediate in the process of nitrification. 2. Nitrous oxide salts used in food preservation.
No Observable Adverse Effect Level (NOAEL)
An exposure level at which there are no statistically or biologically significant increases in the frequency or severity of adverse effects between the exposed population and its appropriate control; some effects may be produced at this level, but they are not considered as adverse, or as precurors to adverse effects. In an experiment with several NOAELs, the regulatory focus is primarily on the highest one, leading to the common usage of the term NOAEL as the highest exposure without adverse effects.
Non-Community Water System
A public water system that is not a community water system; e.g. the water supply at a camp site or national park.
Non-Point Sources
Diffuse pollution sources (i.e. without a single point of origin or not introduced into a receiving stream from a specific outlet). The pollutants are generally carried off the land by storm water. Common non-point sources are agriculture, forestry, urban, mining, construction, dams, channels, land disposal, saltwater intrusion, and city streets.
Non-Transient Non-Community Water System
A public water system that regularly serves at least 25 of the same non-resident persons per day for more than six months per year.
NRC
National Research Council
Nutrient
Any substance assimilated by living things that promotes growth. The term is generally applied to nitrogen and phosphorus in wastewater, but is also applied to other essential and trace elements.
NWRI
National Water Research Institute
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Odor Threshold
The minimum odor of a water or air sample that can just be detected after successive dilutions with odorless water. Also called threshold odor.
Oligotrophic Lakes
Deep clear lakes with few nutrients, little organic matter and a high dissolved-oxygen level.
Operator Certification
Certification of operators of community and nontransient noncommunity water systems, asbestos specialists, pesticide applicators, hazardous waste transporter, and other such specialists as required by the EPA or a state agency implementing an EPA-approved environmental regulatory program.
Organic Matter
Carbonaceous waste contained in plant or animal matter and originating from domestic or industrial sources.
Orifice
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.
Osmosis
The passage of a liquid from a weak solution to a more concentrated solution across a semipermeable membrane that allows passage of the solvent (water) but not the dissolved solids.
Overdraft
The pumping of water from a groundwater basin or aquifer in excess of the supply flowing into the basin; results in a depletion or "mining" of the groundwater in the basin.
Overturn
One complete cycle of top to bottom mixing of previously stratified water masses. This phenomenon may occur in spring or fall, or after storms, and results in uniformity of chemical and physical properties of water at all depths.
Oxidation-Reduction Potential
The electric potential required to transfer electrons from one compound or element (the oxidant) to another compound (the reductant); used as a qualitative measure of the state of oxidation in water treatment systems.
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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 contaminants.
Parameter
A variable, measurable property whose value is a determinant of the characteristics of a system; e.g. temperature, pressure, and density are parameters of the atmosphere.
Particulate Loading
The mass of particulates per unit volume of air or water.
Parts Per Billion (ppb)/Parts Per Million (ppm)
Units commonly used to express contamination ratios, as in establishing the maximum permissible amount of a contaminant in water, land, or air.
Pathogens
Microorganisms (e.g., bacteria, viruses, or parasites) that can cause disease in humans, animals and plants.
Perched Water
Zone of unpressurized water held above the water table by impermeable rock or sediment.
Percolation
1. The movement of water downward and radially through subsurface soil layers, usually continuing downward to ground water. Can also involve upward movement of water. 2. Slow seepage of water through a filter.
Persistence
Refers to the length of time a compound stays in the environment, once introduced. A compound may persist for less than a second or indefinitely.
pH
An expression of the intensity of the basic or acid condition of a liquid; may range from 0 to 14, where 0 is the most acid and 7 is neutral. Natural waters usually have a pH between 6.5 and 8.5.
Phenols
Organic compounds that are byproducts of petroleum refining, tanning, and textile, dye, and resin manufacturing. Low concentrations cause taste and odor problems in water; higher concentrations can kill aquatic life and humans.
Phosphorus
An essential chemical food element that can contribute to the eutrophication of lakes and other water bodies. Increased phosphorus levels result from discharge of phosphorus-containing materials into surface waters.
Phytoplankton
Small, usually microscopic plants (such as algae), found in lakes, reservoirs, and other bodies of water.
Plug Flow
Type of flow the occurs in tanks, basins, or reactors when a slug of water moves through without ever dispersing or mixing with the rest of the water flowing through.
Point Source
A stationary location or fixed facility from which pollutants are discharged; any single identifiable source of pollution; e.g. a pipe, ditch, ship, ore pit, factory smokestack.
Point-of-Use Treatment Device
Treatment device applied to a single tap to reduce contaminants in the drinking water at the one faucet.
Polymer
A chemical formed by the union of many monomers (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.
Pore
A very small open space in a rock or granular material. Also see interstice
Post-Chlorination
Addition of chlorine to plant effluent for disinfectant purposes after the effluent has been treated.
Potentiometric Surface
The surface to which water in an aquifer can rise by hydrostatic pressure.
Prechlorination
The addition of chlorine at the headworks of a treatment plant prior to other treatment processes. Done mainly for disinfection and control of tastes, odors, and aquatic growths, and to aid in coagulation and settling.
Precipitation
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).
Prescriptive
Water rights which are acquired by diverting water and putting it to use in accordance with specified procedures; e.g. filing a request with a state agency to use unused water in a stream, river, or lake.
Pressure Sewers
A system of pipes in which water, wastewater, or other liquid is pumped to a higher elevation.
Primary Drinking Water Regulation
Applies to public water systems and specifies a contaminant level, which, in the judgment of the EPA Administrator, will not adversely affect human health.
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.
Probability of Detection
The likelihood, expressed as a percentage, that a test method will correctly identify a leaking tank.
Process Verification
Verifying that process raw materials, water usage, waste treatment processes, production rate and other facts relative to quantity and quality of pollutants contained in discharges are substantially described in the permit application and the issued permit.
Product Level
The level of a product in a storage tank.
Protocol
A series of formal steps for conducting a test
Public Comment Period
The time allowed for the public to express its views and concerns regarding an action by EPA (e.g. a Federal Register Notice of proposed rule-making, a public notice of a draft permit, or a Notice of Intent to Deny).
Public Water System
A system that provides piped water for human consumption to at least 15 service connections or regularly serves 25 individuals.
Pumping Test
A test conducted to determine aquifer or well characteristics.
Purveyor, Water
An agency or person that supplies water (usually potable water).
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Quality Assurance/Quality Control
A system of procedures, checks, audits, and corrective actions to ensure that all EPA research design and performance, environmental monitoring and sampling, and other technical and reporting activities are of the highest achievable quality.
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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.
Radius of Influence
The radial distance from the center of a wellbore to the point where there is no lowering of the water table or potentiometric surface (the edge of the cone of depression)
Raw Water
Intake water prior to any treatment or use.
Real-Time Monitoring
Monitoring and measuring environmental developments with technology and communications systems that provide time-relevant information to the public in an easily understood format people can use in day-to-day decision-making about their health and the environment.
Receiver
A device which indicates the result of a measurement. 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 indicator.
Recharge
The process by which water is added to a zone of saturation, usually by percolation from the soil surface; e.g., the recharge of an aquifer.
Recharge Rate
The quantity of water per unit of time that replenishes or refills an aquifer.
Reduction
The addition of hydrogen, removal of oxygen, or addition of electrons to an element or compound.
Relative Risk Assessment
Estimating the risks associated with different stressors or management actions.
Remote Sensing
The collection and interpretation of information about an object without physical contact with the object; e.g., satellite imaging, aerial photography, and open path measurements.
Reservoir
Any natural or artificial holding area used to store, regulate, or control water.
Residual
Amount of a pollutant remaining in the environment after a natural or technological process has taken place; e.g., the sludge remaining after initial wastewater treatment.
Residual Disinfectant Concentration ("C" in CT calculations)
The concentration of disinfectant measured in mg/L in a representative sample of water.
Reverse Osmosis
A treatment process used in water systems by adding pressure to force water through a semi-permeable membrane. Reverse osmosis removes most drinking water contaminants. Also used in wastewater treatment. Large-scale reverse osmosis plants are being developed.
Ribonucleic Acid (RNA)
A molecule that carries the genetic message from DNA to a cellular protein-producing mechanism.
Risk
A measure of the probability that damage to life, health, property, and/or the environment will occur as a result of a given hazard.
Risk Communication
The exchange of information about health or environmental risks among risk assessors and managers, the general public, news media, interest groups, etc.
River Basin
The land area drained by a river and its tributaries.
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Sacrificial Anode
An easily corroded material deliberately installed in a pipe or intake to give it up (sacrifice it) to corrosion while the rest of the water supply facility remains relatively corrosion-free.
Safe Water
Water that does not contain harmful bacteria, toxic materials, or chemicals, and is considered safe for drinking even if it may have taste, odor, color, and certain mineral problems.
Salinity
The percentage of salt in water.
Salts
Minerals that water picks up as it passes through the air, over and under the ground, or from households and industry.
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 Water (Also known as gray water)
Water discharged from sinks, showers, kitchens, or other non-industrial operations, but not from commodes.
Saturation
The condition of a liquid when it has taken into solution the maximum possible quantity of a given substance at a given temperature and pressure.
Screening Risk Assessment
A risk assessment performed with few data and many assumptions to identify exposures that should be evaluated more carefully for potential risk.
Secondary Effect
Action of a stressor on supporting components of the ecosystem, which in turn impact the ecological component of concern.
Secure Maximum Contaminant Level
Maximum permissible level of a contaminant in water delivered to the free flowing outlet of the ultimate user, or of contamination resulting from corrosion of piping and plumbing caused by water quality.
Sedimentation
Letting solids settle out of wastewater by gravity during treatment.
Semi-Confined Aquifer
An aquifer partially confined by soil layers of low permeability through which recharge and discharge can still occur.
Sequestration
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 that has been standing for at least 6 hours in a service pipeline and is collected according to federal regulations.
Sewage
The waste and wastewater produced by residential and commercial sources and discharged into sewers.
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 pollutants.
Signal
The volume or product-level change produced by a leak in a tank.
Sink
A place in the environment where a compound or material collects. See reservoir.
Sludge
A semi-solid residue from any of a number of air or water treatment processes; can be a hazardous waste.
SMCLs
Secondary Maximum Contaminant Levels. Secondary MCLs for various water quality indicators are established to protect public welfare.
Soil Erodibility
An indicator of a soil's susceptibility to raindrop impact, runoff, and other erosive processes.
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.
Solubility
The amount of mass of a compound that will dissolve in a unit volume of solution. Aqueous Solubility is the maximum concentration of a chemical that will dissolve in pure water at a reference temperature.
Sounding Tube
A pipe or tube used for measuring the depths of water.
Source-Water Protection Area
The area delineated by a state for a Public Water Supply or including numerous such suppliers, whether the source is ground water or surface water or both.
Specific Conductance
Rapid method of estimating the dissolved solid content of a water supply by testing its capacity to carry an electrical current.
Spill Prevention, Containment, and Countermeasures Plan (SPCP)
Plan covering the release of hazardous substances as defined in the Clean Water Act.
Spring Melt/Thaw
The process whereby warm temperatures melt winter snow and ice. Because various forms of acid deposition may have been stored in the frozen water, the melt can result in abnormally large amounts of acidity entering streams and rivers, sometimes causing fish kills.
Stabilization
Conversion of the active organic matter in sludge into inert, harmless material.
Stakeholder
Any organization, governmental entity, or individual that has a stake in or may be impacted by a given approach to environmental regulation, pollution prevention, energy conservation, etc.
State Management Plan
Under FIFRA, a state management plan required by EPA to allow states, tribes, and U.S. territories the flexibility to design and implement ways to protect ground water from the use of certain pesticides.
Static Water Level
1. 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 in a conduit under pressure.
Storage
Temporary holding of waste pending treatment or disposal, as in containers, tanks, waste piles, and surface impoundments.
Stressors
Physical, chemical, or biological entities that can induce adverse effects on ecosystems or human health.
Submergence
The distance between the water surface and the media surface in a filter.
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
Chlorination with doses that are deliberately selected to produce water free of combined residuals so large as to require dechlorination.
Supernatant
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.
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 hydraulically (flow) over- or underloaded. Also called overflow rate.
Surface Water
All water naturally open to the atmosphere (rivers, lakes, reservoirs, ponds, streams, impoundments, seas, estuaries, etc.)
Surfactant
Abbreviation for surface-active agent. The active agent in detergents that possesses a high cleaning ability.
Susceptibility Analysis
An analysis to determine whether a Public Water Supply is subject to significant pollution from known potential sources.
Suspended Solids
Small particles of solid pollutants that float on the surface of, or are suspended in, sewage or other liquids. They resist removal by conventional means.
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Tertiary Treatment
Advanced cleaning of wastewater that goes beyond the secondary or biological stage, removing nutrients such as phosphorus, nitrogen, and most BOD and suspended solids.
Thermocline
The middle layer of a thermally stratified lake or reservoir. In this layer, there is a rapid decrease in temperatures in a lake or reservoir.
Total Coliform Rule
Published by the USEPA on June 29, 1989 and effective December 31, 1990, the rule set both health goals and legal limits for total coliform levels in drinking water. The rule also details the type and frequency of testing that water systems must do.
Total Maximum Daily Load (TMDL)
A calculation of the highest amount of a pollutant that a water body can receive and safely meet water quality standards set by the state, territory, or authorized tribe.
Total Trihalomethanes (TTHMs)
By-product of drinking water disinfection that could potentially cause liver, kidney or central nervous system problems; increased risk of cancer
Toxic Dose
The dose level at which a substance produces a toxic effect.
Toxicological Profile
An examination, summary, and interpretation of a hazardous substance to determine levels of exposure and associated health effects.
Transmissivity
The ability of an aquifer to transmit water.
Treatment Plant
A structure built to treat water or wastewater.
Trihalomethane (THM)
One of a family of organic compounds named as derivative of methane. THMs are generally by-products of chlorination of drinking water that contains organic material.
Tuberculation
Development or formation of small mounds of corrosion products on the inside of iron pipe. These tubercules roughen the inside of the pipe, increasing its resistance to water flow.
Turbidity
A cloudy condition in water due to suspended silt or organic matter.
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UKDWI
Drinking Water Inspectorate (U.K.)
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.
Underground Sources of Drinking Water
Aquifers currently being used as a source of drinking water or those capable of supplying a public water system. They have a total dissolved solids content of 10,000 milligrams per liter or less, and are not "exempted aquifers."
Upper Detection Limit
The largest concentration that an instrument can reliably detect.
USEPA
U.S. Environmental Protection Agency
UST'S
Underground storage tanks.
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Vadose Zone
The zone between land surface and the water table within which the moisture content is less than saturation (except in the capillary fringe) and pressure is less than atmospheric. Soil pore space also typically contains air or other gases. The capillary fringe is included in the vadose zone.
Vinyl Chloride
A chemical compound, used in producing some plastics, that is believed to be oncogenic.
Viscosity
The molecular friction within a fluid that produces flow resistance.
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 surface.
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Waste
1. Unwanted materials left over from a manufacturing process. 2. Refuse from places of human or animal habitation.
Wastewater
The spent or used water from a home, community, farm, or industry that contains dissolved or suspended matter.
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 Pollution
The presence in water of enough harmful or objectionable material to damage the water's quality.
Water Quality Criteria
Levels of water quality expected to render a body of water suitable for its designated use. Criteria are based on specific levels of pollutants that would make the water harmful if used for drinking, swimming, farming, fish production, or industrial processes.
Water Quality-Based Limitations
Effluent limitations applied to dischargers when mere technology-based limitations would cause violations of water quality standards. Usually applied to discharges into small streams.
Water Solubility
The maximum possible concentration of a chemical compound dissolved in water. If a substance is water soluble it can very readily disperse through the environment.
Water Supply System
The collection, treatment, storage, and distribution of potable water from source to consumer.
Water Treatment Lagoon
An impound for liquid wastes designed to accomplish some degree of biochemical treatment.
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
WaterRF
Water Research Foundation
Watershed Approach
A coordinated framework for environmental management that focuses public and private efforts on the highest priority problems within hydrologically-defined geographic areas taking into consideration both ground and surface water flow.
WEF
Water Environment Federation
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 Injection
The subsurface emplacement of fluids into a well.
Well Plug
A watertight, gastight seal installed in a bore hole or well to prevent movement of fluids.
Wellhead Protection Area
A protected surface and subsurface zone surrounding a well or well field supplying a public water system to keep contaminants from reaching the well water.
Wetlands
An area that is saturated by surface or ground water with vegetation adapted for life under those soil conditions, as swamps, bogs, fens, marshes, and estuaries.
Whole-Effluent-Toxicity Tests
Tests to determine the toxicity levels of the total effluent from a single source as opposed to a series of tests for individual contaminants.
WRC
Water Research Commission (South Africa)
WSAA
Water Services Association of Australia
expand  Y
Yield
The quantity of water (expressed as a rate of flow or total quantity per year) that can be collected for a given use from surface or groundwater sources.
expand  Z
Zone of Aeration
The comparatively dry soil or rock located between the ground surface and the top of the water table.
Zooplankton
Small, usually microscopic animals(such as protozoans), found in lakes and reservoirs.
 

 

 

 

 

 

 

 

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