Water Glossary

A (3) B (2) C (11) D (4) E (1) F (1) G (3) H (1) I (4) J (1) L (2) M (4) O (1) P (4) Q (1) R (4) S (4) T (1) U (1) W (3) X (1) Z (3)
  • Acre-foot (AF)

    A common water industry unit of measurement. An acre-foot is 325,851 gallons, or the amount of water needed to cover one acre with water one foot deep.

  • Act, The

    The Metropolitan Water District Act. State legislation signed into law by the governor on May 10, 1927, effective July 29, 1927. Metropolitan incorporated Dec. 6, 1928.

  • Aquifer

    An underground geologic formation of rock, soil or sediment that is naturally saturated with water; an aquifer stores groundwater.

  • Arsenic

    A naturally occurring element in the environment. Arsenic in drinking water commonly comes from natural sources in the ground, but some can come from industrial pollution. At high concentrations it can cause cancer.

  • BMPs

    Best management practices. Generally, a set of standardized efficiencies. At Met, refers to a set of water conservation measures agreed to by participants in the California Urban Water Conservation Council.

  • Brackish

    A mixture of freshwater and saltwater.

  • California Plan

    Officially "California's draft Colorado River Water Use Plan," also sometimes called the "4.4 Plan." A planning document designed to reduce California's reliance on surplus Colorado River water over the next 15 years through conservation, water transfers, and conjunctive use measures.

  • Call

    To order, request or retrieve stored water; to call upon.

  • CBO

    Community-based organization. Local organization with which Metropolitan works on mutually beneficial programs.

  • Chromium

    A naturally occurring element found in air, soil, water and food.

  • Chromium VI

    Aka "chrome 6." One of the most common species of chromium, chromium VI can be carcinogenic and can constitute anywhere from 7 to 80 percent of the total chromium in drinking water.

  • CII

    Metropolitan's water conservation program for commercial, industrial and institutional entities.

  • Coachella

    Coachella Valley Water District. Primarily agricultural irrigation district receiving Colorado River water through Coachella Canal and serving portions of Riverside, Imperial and San Diego counties north of the Salton Sea. Has priority 3(b) to California's apportionment of Colorado River water, after (1) PVID; (2.) U.S. Bureau of Reclamation's Yuma Project; (3a) Imperial Irrigation District. MWD has fourth priority.

  • CEQA

    California Environmental Quality Act, which requires an assessment of the possible environmental impacts of public projects.

  • Conjunctive Use

    Storing imported water in a local aquifer, in conjunction with groundwater, for later retrieval and use.

  • Cubic foot

    A frequent water industry term of measurement, as in cubic feet per second. One cubic foot (cf) equals 7.48 gallons. A cubic foot per second is 450 gallons per minute.

  • CRA

    Colorado River Aqueduct, built 1933-1941 and owned and operated by the Metropolitan Water District of Southern California.

  • Diemer

    Robert B. Diemer, Metropolitan general manager 1952-1961, after whom Metropolitan filtration plant at Yorba Linda, in Orange County, was named.

  • Domenigoni

    The name of a pioneer family in southwestern Riverside County and of one of the two valleys dammed to create Diamond Valley Lake, Metropolitan's major reservoir near Hemet in southwestern Riverside County.

  • DVL

    Diamond Valley Lake-Metropolitan's major reservoir near Hemet, in southwestern Riverside County.

  • DWR

    California Department of Water Resources. Guides development and management of California's water resources; owns and operates State Water Project and other water-development facilities.

  • EIR

    Environmental impact report; a study and report on the possible effects of a proposed project, and what can be done to avoid or mitigate them.

  • Fallowing

    A program to generate water by paying farmers to fallow land, i.e., not grow crops. The water not used for irrigation is then transferred to urban areas or stored for future use.

  • Gene

    Aka Gene Camp. Small community on the California bank of the Colorado River, near Parker Dam and Lake Havasu, at and around which are located facilities of Metropolitan's Colorado River Aqueduct. Reputedly the first name of a miner who had established "Gene's Camp" at the site.

  • Groundwater

    Water that has percolated into natural, underground aquifers; water in the ground, not water puddled on the ground.

  • Groundwater Recharge or Replenishment

    Pumping or percolating storm water runoff or imported water into an aquifer to replenish its supplies.

  • Hinds

    Julian B. Hinds, Metropolitan general manager 1941-1951, after whom the western-most of the five pumping plants along the Colorado River Aqueduct was named.

  • IICP

    Incremental Interruption and Conservation Plan, which was in effect during the state's 1987-92 drought and was replaced by the WSDM Plan.

  • IID

    Imperial Irrigation District, primarily agricultural irrigation district in Imperial County south of the Salton Sea. Has priority 3(a) to California's apportionment of Colorado River water. Coachella has priority 3(b). MWD has fourth.

  • I/O-Inlet

    outlet facility, as at a reservoir.

  • IRP; Integrated Resources Plan

    The district's plan to ensure reliable water delivery to its customer member agencies despite population growth, dry spells and droughts. The IRP resources mix includes water storage, conservation, best management practices (BMPs), recycling, desalination, and groundwater recovery, among others.

  • Jensen

    Joseph Jensen, Metropolitan board chairman 1949-1974, after whom the Metropolitan filtration plant at Granada Hills, in Los Angeles County, was named.

  • Laguna Declaration

    A Dec. 16, 1952 policy statement by Metropolitan's Board of Directors that it will "provide its service area with adequate supplies of water to meet expanding and increasing needs in the years ahead."

  • Law of the River

    A complex body of laws, court decrees, contracts, agreements, regulations and an international treaty used to govern allocation and management of Colorado River water.

  • MTBE

    methyl tertiary butyl ether. An oxygenate used in California gasoline to help prevent air pollution. The chemical has a long life and has been determined to have polluted lakes, reservoirs and groundwater after leaking from watercraft, underground tanks and pipelines. Required to be phased out by Dec. 31, 2002.

  • Mills

    Henry J. Mills, Metropolitan general manager 1967-1971, after whom Metropolitan filtration plant at Riverside was named.

  • Moab

    A site near Moab, Utah, where a 10.5 million ton mountain of uranium mill tailings (scrap) is leaching pollutants, including uranium, into the nearby Colorado River.

  • Monterey Agreement

    A December 1994 statement of principles to settle disputes over water allocations and operational aspects of the State Water Project, providing greater water management flexibility and financial stability.

  • Ozone

    A gas that is bubbled through water during the treatment processes to kill bacteria.

  • Palo Verde

    Palo Verde Irrigation District, PVID; primarily agricultural irrigation district lying along the Colorado River 110 miles north of Mexico. Has first priority to river water from California's apportionment. MWD has fourth priority.

  • Perchlorate

    A chemical used in manufacturing rocket fuel that has contaminated some Southern California groundwater basins.

  • Potable

    Drinkable water. Nonpotable means nondrinkable.

  • Preferential Rights

    A member agency has a preferential right to a percentage of Metropolitan's available water supply based on a formula established by the Legislature and set forth in Section 135 of the Metropolitan Act. That percentage is equal to the ratio of each member agency's total accumulated payments to Metropolitan's capital costs and operating expenses compared to the total of all member agencies' payments towards those costs, specifically excepting payments for the purchase of water. The Preferential Rights section has never been invoked.

  • Quantification

    Refers to Quantification Settlement Agreement, a proposed agreement among MWD, CVWD and IID to settle a variety of long-standing disputes regarding the priority, use and transfer of Colorado River water within California.

  • Recharge

    Replenishing an aquifer with stormwater or imported water

  • Reclamation

    Historically, a wide-ranging federal program to irrigate arid lands throughout the West. More recently, a euphemism for treating sewage water so it can be reused for nonpotable purposes. See recycled.

  • Recycled

    Wastewater cleaned for re-use, usually for nonpotable purposes such as irrigating landscape and refilling aquifers


    Regional Urban Water Management Plan. State law requires that every urban water retailer and wholesaler prepare and adopt a water management plan every five years. A dictionary of MWD programs, projects and terminology.

  • Salinity

    The scaling or white deposits that accumulate on coffee pots, water heaters and plumbing fixtures resulting from dissolved mineral salts in the water. Also known as total dissolved solids or TDS.

  • Skinner

    Robert A. Skinner, Metropolitan general manager 1962-1967, after whom Metropolitan filtration plant near Winchester, in southwestern Riverside County, was named.

  • Strategic Plan

    The product of a strategic planning process, a comprehensive approach to how Metropolitan does business. The plan's components include a composite rate structure, a resource management plan, the determination of prices and a compatible board governance and management structure with comprehensive ethical standards.

  • SWP

    State Water Project, of which Metropolitan Water District is the largest contractor. Owned and perated by the California Department of Water Resources.

  • ULF

    ultra-low-flow, as in water-saving toilet fixtures. Currently ULF toilets use 1.6 gallons per flush.

  • Wadsworth

    Hiram W. Wadsworth, prominent Pasadena proponent of building an aqueduct to urban Southern California from the Colorado River and a founder of the Metropolitan Water District, after whom the pumping plant at Diamond Valley Lake was named.

  • Weymouth

    F.E. Weymouth, Metropolitan's first chief engineer and general manager, 1929-41; after whom Metropolitan's first treatment plant at La Verne, in Los Angeles County, was named.

  • WSDM Plan

    Water Surplus and Drought Management Plan, developed by Metropolitan and its member agencies in 1998 and 1999, and adopted by the board in April 1999. Replaced IICP. Identifies the expected sequence of resource management actions Metropolitan will take during surpluses and shortages

  • xeriscape

    landscaping that doesn't require a lot of water

  • zanja

    Spanish word for ditch

  • zone of aeration

    the portion of the ground from the Earth's surface down to the water table - the zone of aeration is not saturated with water because its pores are filled partly by air and partly by water

  • zone of saturation

    the portion of the ground below the water table where all the pores in rock, sediment, and soil are filled with water