ACRE-FOOT: A volume of water equal to one foot in depth covering an area of one acre, or 43,560 cubic feet; approximately 325,851 gallons.

AERATION: The addition of air to water or to the pores in soil.

AGRICULTURE: The science, art, and business of cultivating the soil, producing crops and raising livestock (farming).

AQUIFER: An underground layer of sand, gravel, or rock through which water can pass and is stored. Aquifers supply the water for wells and springs.

AUGMENTATION: The process of adding recycled/reclaimed water that has received advanced treatment to an existing raw water supply (such as a reservoir, lake, river, wetland, and/or groundwater basin) that could eventually be used for drinking water after further treatment.

BACKFLOW PREVENTION: Prevention of the flow of any foreign liquids, gases, or substances into the distribution pipelines of a potable water supply; accomplished by an air gap or mechanical backflow obstacle.

BACTERIA: Simple, one-celled microscopic organisms.  Although some bacteria cause diseases (pathogenic bacteria), others are harmless and fill indispensable ecological roles such as decomposers.

BIOFOULING: The formation of bacterial film (biofilm) on fragile reverse osmosis membrane surfaces.

BRACKISH WATER: Water containing dissolved minerals in amounts that exceed normally acceptable standards for municipal, domestic, and irrigation uses. Considerably less saline than seawater.

CLEAN WATER ACT: The federal law that establishes how the United States will restore and maintain the chemical, physical, and biological integrity of the country's waters (oceans, lakes, streams and rivers, groundwater, and wetlands).

CLIMATE: Meteorological conditions, including temperature, precipitation, condensation and wind.

CHLORINATION: The application of chlorine to water generally for the purpose of disinfection, but frequently for accomplishing chemicals such as iron, manganese or taste and odor removal.

CHLORINE: An element (Cl) ordinarily existing as a greenish-yellow gas (Cl2) about 2.5 times as heavy as air. It is commonly used as a disinfectant in water treatment.

CLARIFIER: Unit that separates particles of dirt from the water and deposits it in a sludge pile.

: Obtaining the benefits of water more efficiently, resulting in reduced demand for water. Sometimes called "end-use efficiency" or "demand management."

DAM: A structure built to hold back water.

DISINFECTION: Water treatment which destroys potentially harmful bacteria.

DROUGHT: A long period of below-average precipitation.

ECOSYSTEM: A community of plants and animals and the physical environment in which they live.

EFFLUENT: The water leaving a water or wastewater treatment plant. If effluent has been treated to a high enough standard, it may be considered reclaimed or recycled.

ENDANGERED SPECIES ACT: The federal law that sets forth how the United States will protect and recover animal and plant species whose populations are in dangerous decline or close to extinction. The law protects not only threatened and endangered species but also the habitat upon which species depend.

ENDOCRINE DISRUPTING COMPOUNDS (EDCs): Chemicals that can interfere with the normal hormone function in humans and animals.

ENVIRONMENTAL IMPACT STATEMENT (EIS): Detailed analysis of the impacts of a project on all aspects of the natural environment required by the federal National Environmental Policy Act for federal permitting or use of federal funds.

EPA: Stands for the United States Environmental Protection Agency (USEPA or EPA). The Federal Agency created in 1970 that implements major environmental legislation. EPA's Office of Drinking Water is given the responsibility of establishing federal drinking water regulations and standards (levels of contaminants, which could be present in water without being harmful to man, when the water is consumed).

ESTUARY: The shallow water areas of bays or the mouths of rivers and creeks. This is the place where ocean tides meet and mix with fresh water.

FILTRATION: A process that separates small particles from water by using a porous barrier to trap the particles and allowing the water through.

FINISHED WATER: Treated drinking water that is considered safe and suitable for delivery to consumers.

FLOODPLAIN: Area formed by fine sediments spreading out in the drainage basin on either side of the channel of a river as a result of the river’s fluctuating water volume and velocity.

FLOW RATE: A measure of the volume of water moving past a given point in a given period of time.

GROUNDWATER: Water found below the surface of the earth.

HYDROLOGIC CYCLE: The movement of water as it evaporates from rivers, lakes or oceans, returns to the earth as precipitation, flows into rivers and evaporates again.

IMPORTED WATER: Water that has originated from one hydrologic region and is transferred to another hydrologic region.

INDIRECT POTABLE REUSE (IPR): The blending of advanced treated recycled or reclaimed water into a natural water source (groundwater basin or reservoir) that could be used for drinking (potable) water after further treatment.

INTEGRATED RESOURCE PLANNING (IRP): A method for looking ahead using environmental, engineering, social, financial and economic considerations; includes using the same criteria to evaluate both supply and demand options while involving customers and other stakeholders in the process.

IRRIGATION: Diverting or moving water from its natural course in order to use it.

MAXIMUM CONTAMINANT LEVEL: The highest allowable amount of a constituent in water. Drinking water quality criteria are established by the U.S. Environmental Protection Agency as regulatory standards.

mg/L: Milligrams per liter; a measurement describing the amount of a substance (such as a mineral, chemical or contaminant) in a liter of water. One milligram per liter is equal to one part per million.

MGD: Abbreviation for million gallons per day. This term is used to describe the volume of water treated and discharged from a treatment plant.

MICROFILTRATION: A physical separation process where tiny, hollow, straw-like membranes separate particles from water. It is used as a pretreatment for reverse osmosis.

NONPOTABLE: Water not suitable for drinking.

NONPOTABLE REUSE: Includes all recycled or reclaimed water-reuse applications except those related to drinking water.

NPDES: National Pollutant Discharge Elimination System. A federal permit authorized by the Clean Water Act, Title IV, which is required for discharge of pollutants to navigable waters of the United States, which includes any discharge to lakes, streams, rivers, bays, the ocean, wetlands, storm sewer, or any tributary to any surface water body.

PARTS PER BILLION: A unit frequently used to measure contamination concentration (parts of contamination per billion parts of water). One thousand parts per billion is equal to one part per million.

PARTS PER MILLION: A unit used to measure contamination concentration (parts of contamination per million parts of water). One part per million is equal to one milligram per liter. (This term is becoming obsolete as instruments measure smaller particles.)

PATHOGENS: Disease-causing organisms (generally viruses, bacteria, protozoa, or fungi).

PERCOLATION POND: A pond that allows water to percolate (or seep) through layers of rock and gravel. The water is cleaned as it slowly travels downward and eventually reaches an underground aquifer. The purpose of man-made percolation ponds is both to clean the water and to keep the ground from sinking.

POTABLE: Water that does not contain pollution, contamination, objectionable minerals or infective agents and is considered safe for domestic consumption; drinkable.

POTABLE REUSE: The addition of advanced treated recycled or reclaimed water (purified water) to augment a potable water distribution system.

PRETREATMENT: A process in wastewater treatment where metal screens are used to remove large objects and chunks of debris.

PRIMARY TREATMENT: The first process in wastewater treatment where solid matter is removed.

RAW WATER: Untreated water.

RECLAIMED WATER: Water that is used more than one time before it passes back into the natural water cycle. Wastewater that has been treated to a level that allows for its reuse for a beneficial purpose. Reclaimed water is sometimes another name for recycled water.

RECYCLED WATER: Water that is used more than one time before it passes back into the natural water cycle. Wastewater that has been treated to a level that allows for its reuse for a beneficial purpose. Recycled water is sometimes another name for reclaimed water.

RESERVOIR: A body of water used to collect and store water, or a tank or cistern used to store potable water.

RETROFIT: The process for constructing and separating new potable and recycled/reclaimed pipelines that allow recycled water to be used for nondrinking purposes. A retrofit system separates recycled water from drinking water pipelines.

REUSE: To use again; recycle; to intercept, either directly or by exchange, water that would otherwise return to the natural hydrologic (water) system, for subsequent beneficial use.

REVERSE OSMOSIS: A method of removing salts or other impurities from water by forcing water through a semi-permeable membrane.

SALINITY: Generally, the concentration of mineral salts dissolved in water. Salinity may be measured by weight (total dissolved solids - TDS), electrical conductivity, or osmotic pressure. Where seawater is known to be the major source of salt, salinity is often used to refer to the concentration of chlorides in the water.

SEAWATER INTRUSION: The movement of salt water into a body of fresh water. It can occur in either surface water or groundwater basins.

SECONDARY TREATMENT: Treatment of wastewater to a nonpotable level so that it may be discharged into the natural hydrologic system.

SOIL-AQUIFER TREATMENT: The process of water being purified by percolating through soil and into an underground aquifer.

STORAGE: Water held in a reservoir for later use.

SURFACE WATER: Water located on the earth's surface.

TDS: Total dissolved solids. A quantitative measure of the residual minerals dissolved in water that remain after evaporation of a solution. Usually expressed in milligrams per liter.

TERTIARY TREATMENT: Treatment of wastewater to a level beyond Secondary Treatment but below Potable.

THERMAL HYDROLYSIS PROCESS (THP): A process that heats and pressurizes solids. The pressure cooking breaks down the solids and enhances the process of anaerobic digestion.

TURBIDITY: A measure of suspended solids in water; cloudiness.

ULTRAFILTRATION (UF): A membrane filtration process that falls between reverse osmosis (RO) and microfiltration (MF) in terms of the size of particles removed.

ULTRAVIOLET TREATMENT (UV): The use of ultraviolet light for disinfection.

URBAN RUNOFF: Water from an urban area that neither infiltrates the soil nor is consumed, but flows into a storm sewer or open waterway.

WASTEWATER: Water that has been previously used by a municipality, industry, or agriculture and has suffered a loss of quality as a result of use.

WATER CYCLE: The movement of water as it evaporates from rivers, lakes or oceans, returns to the earth as precipitation, flows into rivers and evaporates again.

WATERSHED: An area from which water drains and contributes to a given point on a stream or river.

WETLANDS: Areas with standing water or a high water table that under normal circumstances support vegetation typically adapted to saturated soil conditions; generally includes swamps, marshes, bogs and areas with vegetation that grows in or around water.

XERISCAPE: Landscaping concept that requires less water on vegetation that is suited to soils and climate.

µg/L (micrograms per liter): a measurement describing the amount of a substance (such as a mineral, chemical or contaminant) in a liter of water. It is expressed in terms of weight per volume. One µg/L is equal to one part per billion.