Water Glossary



  • acre-foot: Approximately 326,000 gallons; roughly equal to the amount of water a family of four uses in and around the home in a two-year period; the amount of water it would take to cover an acre of land one foot deep.
  • allotment: a share or portion.
  • aqueduct: a structure used to transport water from remote areas to large urban centers.
  • aquifer: an underground space where water collects.
  • artesian aquifer: a confined aquifer where water is contained under great pressure between two impermeable layers.


  • bacteria: a single-celled microscopic organism.
  • bog: a wetland covered by a shallow layer of water, or no visible water at all, and containing ground that is made of sphagnum moss.
  • bottom life: animals that live on the bottom of a healthy body of water.
  • brackish water: Refers to water with a mineral content in the general range between freshwater and seawater.
  • brine: the by-product of desalinating water, about twice the salinity of seawater.


  • California Aqueduct: a 444-mile structure that transports water from the San Francisco/San Joaquin Delta to Southern California.
  • Clean Water Act of 1972: a law that requires the federal government to regulate the quality of the nation’s water supply.
  • Colorado River Aqueduct: a 242-mile structure that transports water from the Colorado River to Southern California.
  • Comprehensive Environmental Response, Compensation and Liability Act of 1980 (Superfund): a law enacted by the federal government to clean up hazardous waste sites that threaten groundwater resources.
  • condensation: water vapor or gas forming a cloud prior to becoming a liquid again.
  • confined aquifer: an aquifer found between two impermeable layers.
  • conservation: saving water and other natural resources.


  • dam: a structure used to hold back the flow of water.
  • desalination: a process that removes dissolved salts from salty or brackish water.
  • dike: a structure used to confine or control water.
  • disinfection: a process in which chlorine and other chemicals are added to water to kill harmful microorganisms.
  • diversion canal: a structure used to change the directional flow of water.


  • entrainment: the incorporation of all life stages of fish and shellfish with intake water flow entering and passing through a cooling-water intake structure and into a cooling-water system.
  • estuary: an area where a river empties into an ocean or sea.
  • evaporation: water turned into a vapor or gas and rising into the atmosphere.


  • filtration: a process that separates small particles from water by using a porous barrier to trap the particles and allowing the water through.
  • fish: a vertebrate (animal with a spine) that lives in water.
  • flocculation: a process in which a chemical such as alum or ferric chloride is added to water to cause dirt and other small particles to join together into “floc” or large clumps.


  • groundwater: water that is stored in aquifers. Aquifers are replenished naturally with rainfall or snowpack or artificially through recharge basins with imported or recycled water.


  • hydrologic cycle: a three-step process by which Earth is continuously able to recycle its water.


  • impingement: the entrapment of all life stages of fish and shellfish on the outer part of an intake structure or against a screening device during periods of intake water withdrawal.
  • imported water: water transported to our region from Northern California or the Colorado River Aqueduct.


  • levee: a raised structure used to contain water and prevent flooding.
  • Los Angeles Aqueduct: a 335-mile structure that transports water from the eastern Sierra Nevada to the City of Los Angeles.


  • mangrove swamp: tropical and subtropical saltwater swamp that contains a species of saltwater tolerant tree or shrub.
  • marsh: a wetland that is wet throughout the year and found at the edge of a river, lake or pond.
  • micro-filtration: a membrane filtration process in which water passes through small pores of the micro-filtration membrane, accumulating particles on its surface. Periodically, flow is reversed to remove the debris. In ocean-water desalination, it is designed to remove particulate matter from seawater to allow the downstream reverse osmosis desalination process to efficiently remove dissolved salts.


  • non-potable water: water not suitable for drinking. Can be used for landscaping, irrigation and industrial uses.
  • non-point pollution source: pollution that comes from various sources not easily identified.


  • Ogalla Aquifer: the largest aquifer in the United States, located in the Midwest.
  • organism: a living plant or animal.
  • oxygen: a gas upon which most life depends.


  • potable water: water that is suitable for drinking.
  • peak flow: highest flow level of a body of water.
  • permeability: a measurement of how freely water moves between pieces of soil and rock.
  • phytoplankton: microscopic free-floating green plants.
  • point pollution source: pollution that comes from an easily identified source.
  • porosity: a measurement of the amount of water held between pieces of soil and rock.
  • Porter-Cologne Water Quality Act: a California law that gives the State Water Resources Control Board ultimate authority over water rights and water control policy.
  • precipitation: water falling to Earth as rain, sleet, snow or hail.
  • 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.


  • recycled water: domestic wastewater purified through primary, secondary and tertiary treatment. Recycled water is ideal for most non-drinking water purposes such as landscaping, irrigation and industrial uses.
  • reservoir: a man-made storage facility used to hold water until it is needed.
  • reverse osmosis: a filtration process that forces water through membranes that contain microscopic holes, removing microorganisms, organic chemicals and inorganic chemicals, producing very pure water.


  • Safe Drinking Water Act of 1974: a law enacted by the federal government that regulates the nation’s drinking water.
  • saltwater marsh: a wetland that is wet throughout the year and found at the edge of a saltwater body.
  • secondary treatment: the second process in wastewater treatment where microorganisms are used to digest organic particles.
  • sediment: mud, sand or gravel that has settled to the bottom of a body of water.
  • sedimentation: a process in which gravity causes small particles to settle to the bottom of a tank or basin.
  • semi-arid: a mostly dry region that gets a small amount of precipitation.
  • Superfund: see Comprehensive Environmental Response, Compensation and Liability Act.
  • surface water: a body of water easily seen as it flows downhill to where it collects.
  • swamp: a wetland that can alternate between being wet and dry for periods of time throughout the year.


  • tertiary treatment: the third process in wastewater treatment where remaining small particles are filtered out of the water before disinfection.
  • Title 22: a section of the California Code of Regulations pertaining to various aspects of drinking water and recycled water standards.
  • turbidity: cloudy or muddy looking water caused by suspended or stirred up particles in the water.


  • Ultra-Low-Flush Toilet: often referred to as ULFTs, these fixtures require only 1.6 gallons of water per flush. These conservation devices save a typical household 7,900 to 21,700 gallons of water each year.
  • unconfined aquifer: an aquifer found close to Earth’s surface that allows water to seep into it.


  • water conservation: the best tool for stretching water supplies without making unnecessary investments in infrastructure, shifting available water resources or negatively impacting the environment.
  • watershed: an area of land where water drains from the higher elevation points into a larger body of water or into the soil.
  • water table: the top surface of a body of groundwater.
  • well: a hole dug into the ground that begins at the surface and ends where it reaches the water.
  • West Coast Basin Aquifer: an aquifer that underlies the Southern California communities of West Basin Municipal Water District within its territories.
  • wetland: an area of land that is wet for a period of time during the year.


  • zooplankton: microscopic free-floating animals.

*For additional definitions, please visit the California Department of Water Resources.

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