Glossary of Water Terms

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Abandoned well—A well whose use has been permanently discontinued or which is in a state of disrepair such that it cannot be used for its intended purpose.

—Reducing the degree or intensity of, or eliminating, pollution.

Acid—A substance that has the ability to react with bases to form salt. The pH of an acidic solution is less than 7. pH 7 is neutral (e.g., pure water)- acids are pH 0 to less than 7. Similarly, bases are greater than 7 to 14. The usual definition of an acid is “any substance that can donate a hydrogen ion”.

Acid Deposition ("acid rain")
—Water that falls to or condenses on the Earth's surface as rain, drizzle, snow, sleet, hail, dew, frost, or fog with a pH of less than 5.6.

Acidic—The condition of water or soil which contains a sufficient amount of acid substances to lower the pH below 7.0.

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. An acre-foot serves annual needs of two typical California families.

Acrylamide (CH2CHCONH2)—An organic monomer used as a starting material for polymers that are used as coagulants or filter aids. Its concentration in finished drinking water is controlled by limiting the allowable dose of polymer that can be added to water.

The Act—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.

Active Ingredient—The component which kills or otherwise controls, targets pests in any pesticide product. Pesticides are regulated primarily on the basis of active ingredients.

Adjudication—A court determination of water rights for a groundwater basin or a stream; adjudication sets priorities during shortages.

Aeration—The addition of air to water or to the pores in soil.

Age Tank—A tank used to store a known concentration of a chemical solution for feed to a chemical feeder. Also known as a day tank.

Agricultural Pollution—The liquid and solid wastes from farming, including: runoff and leaching of pesticides and fertilizers; erosion and dust from plowing; animal manure and carcasses; crop residue; and debris.

Algae—Microscopic plants which contain chlorophyll and float or suspend in water. Excess algae growths can impact tastes and odors to potable water. Their biological activities affect the pH and dissolved oxygen of the water.

Alkali—Any of certain soluble salts, principally of sodium, potassium, magnesium, and calcium, that have the property of combining with acids from neutral salts and may be used in chemical water treatment processes.

Alkaline—The quality of being bitter due to alkaline content (pH is greater than 7).

Alum (Al2(SO4)3·14 H2O)—The common name for aluminum sulfate, a chemical used in the coagulation process to remove particles from water.

Aluminum (Al)—A metallic element. Aluminum is the most abundant metal in the earth’s crust; it does not occur free in nature.

Aqueduct— Man-made canal or pipeline used to transport water.

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.

Assay—A test for a particular chemical or effect. 



Bacterium—A microscopic unicellular organism that lacks a nuclear membrane. Some can cause disease.

Bacteria—Plural of bacterium.

—A 10- to 20-foot-long pipe equipped with a valve at the lower end. It is used to remove slurry from the bottom or the side of a well as it is being drilled.

—A substance that has a pH value between 7 and 14.

Bedrock—The solid rock that underlies all soil, sand, clay, gravel and other loose materials on the earth's surface. Unfractured bedrock is impermeable while fractured bedrock may store and transmit groundwater.

Blackwater—Water that contains animal, human or food wastes.

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.

Bond—A promise to repay money borrowed, plus interest, over a specified period of time.

Bond Issue—A means of raising large amounts of money for major projects by selling bonds.

Brackish—A mixture of freshwater and saltwater.

Buffer—A solution or liquid whose chemical makeup neutralizes acids or bases without a great change in pH.



California Environmental Quality Act (CEQA)—Requires an assessment of the possible environmental impacts of projects.

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.

Capillarity—The process by which water rises through rock, sediment or soil caused by the cohesion between water molecules and an adhesion between water and other materials that "pulls" the water upward.

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

CUWCC—California Urban Water Conservation Council. Created to increase efficient water use statewide through partnerships among urban water agencies, public interest organizations and private entitites. The Council's goal is to integrate urban water conservation Best Management Practices into the planning and management of California's water resources.

Centrifuge—A mechanical device that uses centrifugal or rotational forces separate substances of different densities, such as solids from liquids or liquids from other liquids.

Cesspool—A covered hole or pit for receiving sewage.

CFS—Cubic Feet Per Second.

Chloramination—the treatment of a substance, such as drinking water, with chlorine and ammonia (chloramines) in order to kill disease-causing organisms.

Chloride (Cl–)—One of the major anions commonly found in water and wastewater. Its presence is often determined by ion chromatographic or volumetric analysis. Consumers who drink water with concentrations of chloride exceeding a secondary maximum contaminant level of 250 milligrams per liter may notice a salty taste.

Chlorination— The treatment of a substance, such as drinking water, with chlorine in order to kill disease-causing organisms.

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 is known to cause cancer through exposure to airborne chromium compounds in industrial settings. The evidence of its carcinogenicity by ingestion is not compelling. The U.S. Environmental Protection Agency determined that chromium VI was not carcinogenic by ingestion.

Clarity—Clearness of liquid, as measured by a variety of methods.

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.

Coagulation—The process, such as in treatment of drinking water, by which dirt and other suspended particles become chemically “stuck together” so they can be removed from water.

Coliform bacteria—Bacteria of the family Enterobacteriaceae, commonly found in the intestinal tracts of warm-blooded animals. In sanitary bacteriology, these organisms are defined as all aerobic and facultative anaerobic, gram-negative, nonspore-forming, rod-shaped bacteria that ferment lactose with gas and acid formation within 48 hours at 95° Fahrenheit (35° Celsius).

Color—A physical characteristic describing the appearance of water (different from turbidity, which is the cloudiness of water). Color is frequently caused by fulvic and humic acids.

Combined Sewers—A sewer system that carries both sewage and storm-water runoff.

Condensation—Water vapor changing back into liquid.

Condensation Surfaces—Small particles of matter, such as dust and salt suspended in the atmosphere, which aid the condensation of water vapor in forming clouds.

Confined Aquifer—An aquifer that is bound above and below by dense layers of rock and contains water under pressure.

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

Contour Plowing—Plowing done in accordance with the natural outline or shape of the land by keeping the furrows or ditches at the same elevation as much as possible to reduce runoff and erosion.

Control—(1) A condition in which specific quality criteria have been achieved in a laboratory analysis. (2) A type of sample used to assess the quality of an analytical process.

Corrosivity—An indication of the corrosiveness of water. The corrosiveness of water is described by the water’s pH, alkalinity, hardness, temperature, total dissolved solids, dissolved oxygen concentration, and
Langelier saturation index.

Cost Effective—Able to at least pay for itself or make a profit.

County Water Authority—A public water district serving a county-wide area.

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

Cryptosporidium—A group of widespread intestinal coccidian protozoan parasites about 5 micrometers in diameter, causing diarrhea and capable of infecting humans, birds, fish, and snakes. It is responsible for waterborne disease outbreaks.

CRWUA—Colorado River Water Users Association. CRWUA is a non-profit, non-partisan organization, formed to plan, study, formulate and advise on ways to protect and safeguard the interests of all whom use the Colorado River.

CT—The product of disinfectant concentration (in milligrams per liter) determined before or at the first customer and the corresponding disinfectant contact time (in minutes). It is also called the CT value. Units are milligram minutes per liter.

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.

CUWA—California Urban Water Agencies. Group of 11 member agencies serving two-thirds of state's population.

CVP—Central Valley Project. A series of dams, reservoirs and canals in the San Joaquin Valley of California.

Cyst—The infectious stage for Giardia, 7 to 10 micrometers long and refractile to light when viewed with a brightfield microscope.











Delta—Fan-shaped area at the mouth of a river.

Deposition—The process of dropping or getting rid of sediments by an erosional agent such as a river or glacier; also called sedimentation.

—The process of removing salt from seawater or brackish water.

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

Discharge—the amount of water flowing past a location in a stream/river in a certain amount of time - usually expressed in liters per second or gallons per minute.

Disinfectant—An agent that destroys or inactivates harmful microorganisms.

Disinfection By-Product (DBP)—A chemical by-product of the disinfection process. Disinfection by-products are formed by the reaction of the disinfectant, natural organic matter, and the bromide ion (Br–). Some disinfection by-products are formed through halogen (e.g., chlorine or bromine) substitution reactions; i.e., halogen-substituted by-products are produced. Other disinfection by-products are oxidation by-products of natural organic matter (e.g., aldehydes—RCHO). Concentrations are typically in the microgram-per-litre or nanogramper-litre range.

Disinfection By-Product Precursor (DBPP)—A substance that can be converted into a disinfection by-product during disinfection. Typically, most of these precursors are constituents of natural organic matter. In addition, the bromide ion (Br–) is a precursor material. See also bromide; disinfection by-product; natural organic matter.

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.

DRIP—Desalination Research and Innovation Partnership. A landmark research partnership among the water and electric industries, state and federal agencies and academia.

Drought—A prolonged period of below-average precipitation.

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.




Ecosystem—An interacting network of groups of organisms together with their nonliving or physical environment.


Effluent—Water flowing from a structure such as a treatment plant. Contrast with influent.1Effluent—Water flowing from a structure such as a treatment plant. Contrast with influent.

—Environmental Impact Report; a state-mandated written summary of the positive and negative effects on the environment caused by the construction and operation of a project.

Endangered Species—A species of animal or plant threatened with extinction.

Epichlorohydrin (chloropropylene oxide, C3H5OCl) —A highly volatile, unstable liquid epoxide. It is a major raw material for epoxy and phenoxy resins and has other industrial uses. It is a treatment chemical that is regulated in drinking water under the Phase II Rule for synthetic organic contaminants and inorganic contaminants.

Erosion—The processes of picking up, moving, shaping and depositing sediments by various agents; erosional agents include streams, glaciers, wind and gravity.

Escherichia coli (E. coli)—A gram-negative, facultatively anaerobic, nonspore-forming bacillus commonly found in the intestinal tracts of humans and other warm-blooded animals. In sanitary bacteriology, Escherichia coli is considered the primary indicator of recent fecal pollution.

Evaporation—Water changing into vapor and rising into the air.




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.


Fecal Coliform (FC)—Members of the total coliform group of bacteria that are characterized by their ability to ferment lactose at 112.1° Fahrenheit (44.5° Celsius) and that are considered more specific indicators of fecal contamination than are coliforms that ferment lactose only at 95° Fahrenheit (35° Celsius). Escherichia coli and some Klebsiella pneumoniae strains are the principal fecal coliforms.1

FERC—Federal Energy Regulatory Commission. An independent regulatory agency within the Department of Energy.

Ferric Chloride (FeCl3)—An iron salt used as a coagulant in water treatment. The iron has a valence of +3

Filtration—passing water through coal, sand and gravel to remove particles.

Fish Ladder—A device to help fish swim around a dam.

Fishery—The aquatic region in which a certain species of fish lives.

Floc—Clumps of impurities removed from water during the purification process; formed when alum is added to impure water.

Flocculation—A step in water filtration in which alum is added to cause particles to clump together.

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.

Fluoride Ion (F–)—A halide ion. Fluoride salts are added to drinking water for fluoridation. Fluoride is regulated by the US Environmental Protection Agency.





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.

Giardia—The genus name for a group of single-celled, flagellated, pathogenic protozoas found in a variety of vertebrates, including mammals, birds, and reptiles. These organisms exist either as trophozoites or as cysts, depending on the stage of the life cycle.

Glacial StriationsLines carved into rock by overriding ice, showing the direction of glacial movement.

Gross Alpha (a) Particle Activity The total radioactivity caused by alpha particle emission as inferred from measurements on a dry sample. It is regulated by the US Environmental Protection Agency.

Gross Beta (b) Particle Activity The total radioactivity caused by beta particle emission as inferred from measurements on a dry sample. It is regulated by the US Environmental Protection Agency.1

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.





Haloacetic Acid (HAA)—(CX3COOH, where X = Cl, Br, H in various combinations) A class of disinfection by-products formed primarily during the chlorination of water containing natural organic matter. When bromide (Br–) is present, a total of nine chlorine-, bromine-and-chlorine-, or bromine-substituted species may be formed. Trihalomethanes and haloacetic acids are the two most prevalent classes of by-products formed during chlorination; and subject to regulation under the Disinfectant/Disinfection by-products rule.

Hardness—A characteristic of water determined by the levels of calcium and magnesium.

Heterotrophic Plate Count (HPC) —A bacterial enumeration procedure used to estimate bacterial density in
an environmental sample, generally water. Other names for the procedure [within the water industry] include total plate count, standard plate count, plate count, and aerobic plate count.

—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.

Hydroelectric Planta power plant that produces electricity from the power of rushing water turning turbine-generators.

Hydrologythe scientific study of the behavior of water in the atmosphere, on the Earth's surface and underground.




ICP—Innovative Conservation Program. The Innovative Conservation Program portion is designed to provide grants to explore the water savings potential and practicality of new water conserving technologies. Special consideration will be given to projects promoting water-landscape saving products or technologies.

—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.


Immunofluorescence—The emission of visible light by a compound that has been irradiated with ultraviolet light. For example, a fluorescent compound (i.e., a fluorescein) can be attached to an antibody. Bacterial, viral, or other antigens that react with the antibody can then be observed by illuminating the sample with ultraviolet light.

—Inlet-outlet facility at a reservoir.

Inorganic—Pertaining to material such as sand, salt, iron, calcium salts, and other mineral materials. Inorganic substances are of mineral origin, whereas organic substances are usually of animal or plant origin and contain carbon.

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.

Irrigation—Supplying water to agriculture by artificial means, such as pumping water onto crops in an area where rainfall is insufficient.

ISP—Innovated Supply Program. The ISP will provide up to a total of $250,000 in grants on a competitive basis to stimulate and advance new innovative ideas that have potential to produce new sources of water supply for Southern Californa.




Jensen—Joseph Jensen, Metropolitan board chairman 1949-1974, after whom the Metropolitan treatment 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.

Leach—To remove components from the soil by the action of water trickling through.

Legionella—A genus of bacteria of the family Legionellaceae. It currently consists of at least 51 serogroups comprising 34 species.1 It has the ability to colonize water in distribution systems (heating tanks, cooling towers, air conditioning lines, etc). It can cause disease in humans (e.g., Legionnaires’ disease or Legionellosis) that is progressive and sometimes fatal, or a milder form of pneumonic illness (Pontiac fever) that is self-limited (i.e., heals on its own) with respiratory symptoms similar to influenza. 





MAF—Million acre-feet.

Marginal Land
—Land which, in its natural state, is not well suited for a particular purpose, such as raising crops.

MCL—Maximum Contaminant Level. According to health agencies, the maximum amount of a substance that can be present in water that's safe to drink and which looks, tastes and smells good.

Member Agency
—One of 26 member public water providers associated with the Metropolitan Water District of Southern California, from which it purchases water and on whose board it is represented.

—Million gallons per day, a measure used for water treatment plants and other facilities.

Microbiological—Relating to microorganisms and their life processes.

Microorganism—An organism of microscopic size, such as bacterium.

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

Mitigation—A way in which an agency may offset negative environmental impacts of a project or make the impacts less serious.

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.

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.

Mulch—Material spread on the ground to reduce soil erosion and evaporation of water; include hay, plastic sheeting and wood chips.

Municipal Water District—A public water provider governed by a locally elected board of directors, which supplies water to the public directly or through subagencies.

MWQI—Municipal Water Quality Investigation. Government agencies conduct water quality studies in the Sacramento watershed, the Sacramento-San Joaquin Delta, and the San Francisco Bay Area.




Natural Environment—All living and nonliving things that occur naturally on the earth.

Nitrate (NO3–)—An oxidized ion of nitrogen. Nitrifying bacteria can convert nitrite (NO2–) to nitrate in the nitrogen cycle. Sodium nitrate (NaNO3) and potassium nitrate (KNO3) are used as fertilizer. The nitrate ion is regulated by the US Environmental Protection Agency.

Nitrite (NO2–)—An intermediate oxidized ion of nitrogen. Nitrifying bacteria can convert ammonia (NH3) to nitrite (NO2–) to nitrate (NO3–) in the nitrogen cycle. Sodium nitrite (NaNO2) is used in curing meats. The nitrite ion is regulated by the US Environmental Protection Agency.

Nonpoint Source Pollution—Pollution which comes from diffuse sources such as urban and agricultural runoff.

NWRA—National Water Resources Association. Advocates federal policies, legislation and regulations promoting the development, management, protection and beneficial use of water resources.



Odor Threshold—The minimum odor of a water sample that can just be detected after successive dilutions with odorless water.1 The odor threshold is reported as the threshold odor number.

Oocyst—A structure that is produced by [some] coccidian protozoa (i.e., Cryptosporidium) as a result of sexual reproduction during the life cycle. The oocyst is usually the infectious and environmental stage, and it contains sporozoites. For the enteric protozoa, the oocyst is excreted in the feces.

Organic Chemical—A chemical having a carbon–hydrogen structure.

Ozone—A gas derived from oxygen that is bubbled through water during the treatment processes to kill microorganisms. 



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.

Parameter—A water quality attribute. For example, the presence of certain bacteria, the hardness, and the level of sodium are all parameters.

Pathogen—an infectious agent. An organism capable of causing infection or infectious disease.

Perchlorate—A chemical used in manufacturing rocket fuel that has contaminated some Southern California groundwater basins. Perchlorate interferes with the iodide uptake into the thyroid gland. The disruption of thyroid functions leads to changes in metabolism in adults and normal growth and development in children.

Perennial Yield—Maximum quantity of water that can be annually withdrawn from a groundwater basin over a long period of time (during which water supply conditions approximate average conditions) without developing an overdraft condition.

PEROXONE—A combination of peroxide and ozone used to kill germs and oxidize taste-and-odor compounds in water.

pH—A relative scale of how acidic or basic (alkaline) a material is; the scale goes from 0 to 14; 7 is neutral, acids have pH values less than 7 and bases have pH values higher than 7.

Pipeline—Carries water above or underground to homes and businesses.

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.

Protozoan—Single-celled, animal-like, eukaryotic organisms of the kingdom Protista. Protozoans can occur wherever moisture exists. There are many parasites and commensals of plants and animals, as well as free-living species. They cause a number of diseases, such as African sleeping sickness, malaria, and dysentery. They are an economically and scientifically important group. It is thought that the organisms of the kingdom Animalia evolved from ancestors which were protozoans.

Pumping Lift—Distance water must be lifted in a well from the pumping level to the ground surface.

Pumping Plant—Facility that lifts water up and over the hills.




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.



Radionuclide—A material with an unstable atomic nucleus that spontaneously decays or disintegrates, producing radiation.

Radium (Ra)—A naturally occurring radioactive element (in the form of radium-226 or radium-228) created in the decay of the uranium and thorium series. Radium can be removed from water by cation exchange

Radium-226 + Radium-228 (Ra-226 + Ra-228)—The sum of the naturally occurring radioactive isotopes of radium. The regulation for radium by the US Environmental Protection Agency is for the sum of the [two] isotopes.

Recharge—Replenishing an aquifer with stormwater or imported water

Reclaimed Water—Wastewater that has been cleaned so that it can be reused for most purposes except drinking.

—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.

Reservoirs—A pond or lake where water is collected and stored until it is needed.

Residuals—Any gaseous, liquid, or solid by-product of a treatment process that ultimately must be disposed of. For example, in a fixed-bed filter for removing particles from water, both the filter backwash water and the solids in the backwash water are residuals.

Rills—Small grooves, furrows, or channels in soil made by water flowing down over its surface; also another name for a stream-usually a small stream.

Runoff—Liquid water that travels over the surface of the Earth, moving downward due to the law of gravity; runoff is one way in which water that falls as precipitation returns to the ocean.

RUWMP—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.



SCAG—Southern California Association of Governments. It has evolved as the largest of nearly 700 councils of government in the United States, functioning as the Metropolitan Planning Organization for six counties. As the designated Metropolitan Planning Organization, the Association of Governments is mandated by the federal government to research and draw up plans for transportation, growth management, hazardous waste management and air quality. Additional mandates exist at the state level.

—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 treatment plant near Winchester, in southwestern Riverside County, was named.

Source water— The supply of water for a water utility. Source water is usually treated before distribution to consumers, but some groundwaters are of such a quality that they can be distributed untreated. This term is preferred over raw water.

Specific Conductance—A measure of the ability of a solution to conduct electrical current. Its value is inversely proportional to the solution’s electrical resistance. The conductivity value is commonly used in water-desalting processes as a means to evaluate desalting efficiency and to estimate the total dissolved solids concentration; the conductivity value of a water sample is multiplied by an empirical factor representative of the typical total dissolved solids/conductivity ratio for the specific type of water. The units of conductivity are often reported as micromhos per centimetre at 25° Celsius, but this is not a Système International unit; multiplying such a value by 10–4 converts the value to units of siemens per meter.

Standard—(1) A recommended practice in the manufacturing of products or materials or in the conduct of a business, art, or profession. Such standards may or may not be used as (or called) specifications. (2) A
document that specifies the minimum acceptable characteristics of a product or material, issued by an organization that develops such documents (e.g., an American Water Works Association standard). (3) A numerical contaminant limit set by a regulatory agency (e.g., a US Environmental Protection Agency maximum contaminant level).

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.

Sulfate (SO42–)—An inorganic ion that is widely distributed in nature. It may be present in natural waters in concentrations ranging from a few to several thousand milligrams per liter.

Surface Runoff—Water flowing along the ground into rivers, lakes and oceans.

Surface Water—All water, fresh and salty, on the Earth's surface.

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

SWRCB—State Water Resources Conrol Board. Regulates water quality and water rights to protect beneficial water use in the Bay/Delta estuary.



THMLs—Total trihalomethanes. By-products of chlorination.

—The top layer of soil; topsoil can grow better crops partly because it has more organic matter (humus), allowing it to hold more water than lower soil layers.

Total Chlorine Residual—The total amount of chlorine residual present after a given contact time in a water sample, regardless of the type of chlorine. See also residual chlorine; total chlorine.

Total Coliform Rule (TCR)—A rulemaking of the US Environmental Protection Agency that sets National Primary Drinking Water Regulations for total coliforms, fecal coliforms, and Escherichia coli. The rule was promulgated June 29, 1989 (54 Federal Register 27544–27568) and amended Jan. 15, 1991 (56 Federal Register 1556–1557).1

Total Coliforms (TC)—The group of bacteria used as warm-blooded animal fecal pollution indicator organisms of drinking water quality. Total coliforms are regulated by the US Environmental Protection Agency.

Total Dissolved Solids (TDS) —The weight per unit volume of filtered water. The liquid passing the filter are evaporated to dryness. The filter pore diameter and evaporation temperature are frequently specified.

Total Organic Carbon (TOC)—A measure of the concentration of organic carbon in water, determined by oxidation of the organic matter into carbon dioxide (CO2). TOC includes all the carbon atoms covalently bonded in organic molecules. Most of the organic carbon in drinking water supplies is dissolved organic carbon, with the remainder referred to as particulate organic carbon. In natural waters, total organic carbon is composed primarily of nonspecific humic materials. Total organic carbon is used as a surrogate measurement for disinfection by-product precursors, although only a small fraction of the organic carbon will react to form these by-products. Quantitatively, total organic carbon is determined by removing interfering inorganic carbon, such as bicarbonate (HCO3–), and oxidizing the organic carbon to carbon dioxide. Typically, the carbon dioxide is then measured with a nondispersive infrared detector.

Total Trihalomethanes (TTHM) —The sum of the four chlorine and bromine-containing trihalomethanes (i.e., chloroform, bromodichloromethane, dibromochloromethane, and bromoform). The US Environmental Protection Agency regulates the sum of these four species on a weight concentration basis.

Transpiration—Evaporation of water through the leaves of plants.

Trihalomethanes—Organic compounds which may be harmful to health at certain levels in drinking water.

Turbidity—The state of having sediment or foreign particles suspended or stirred up in water.



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

Unconfined Aquifer—An aquifer that discharges and recharges with an upper surface that is the water table.

Uranium (U) —A metallic element that is naturally occurring with three main radioactive isotopes (i.e., U-234, U-235, and U-238). Uranium is carcinogenic and can also cause damage to the kidney. Total uranium is regulated by the US Environmental Protection Agency.

Usable Storage Capacity—The quanitity of groundwater of acceptable quality that can be economically withdrawn from storage.

USBR—United States Bureau of Reclamation.

UWI—Urban Water Institute. This organization provides programs and publications geared to policy makers who can no longer afford to be uninformed on water, wastewater, flood control, runoff and environmental issues.


Virus—(1) A minute organism not visible by light microscopy. A virus is an obligate parasite dependent on nutrients inside cells for its metabolic and reproductive needs. It consists of a strand of either deoxyribonucleic acid or ribonucleic acid, but not both, [inside] a protein covering called a capsid. 



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.

Wash Water—Water that is used to clean a unit process. Wash water is typically identified as backwash water and is associated with the wastewater resulting from the cleaning of filter media to remove attached particles.

Wastewater—Water that has waste material in it.

Water Cycle—The movement of water from the air to and below the Earth's surface and back into the air.

Water Reclamation—Treating wastewater so that it can be used again.

Watershed—A geographical portion of the Earth's surface from which water drains or runs off to a single place like a river; also called a drainage area.

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


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