Education Central




Link to the definition of Acre-foot

A measurement for water equaling approximately 326,000 gallons. Enough water to fill a football field to a depth of one foot or to supply the water needs of a family of four for two years.


Link to the definition of Adjudicated

The court decides who is allowed to pump from the groundwater basin and how much annually can be pumped. The amount pumped is dependent upon the condition of the basin. The court also designates a water master to oversee adjudication. The Orange County Groundwater Basin is a non-adjudicated basin. An example of an adjudicated basin is the central basin.

Amber-Colored Water 

Link to the definition of Amber-Colored Water

Water from the groundwater basin that has the color of weak tea, a slight sulfur odor and slightly elevated temperature. The color and odor are believed to result from ancient redwood forests leaching into the basin. Amber-colored water is found in aquifers below the clear water zone. In Mesa Water's service area, amber-colored water is found below 600 ft. with the elimination of aesthetic characteristics (color, odor) and meets all State and Federal water quality standards.


Link to the definition of Aqueducts

Canals used to carry water from a great distance.


Link to the definition of Aquifer

A natural underground layer of porous, water-bearing materials (sand, gravel) usually capable of yielding a large amount or supply of water.


Link to the definition of Artesian

Water held under pressure in porous rock or soil confined by impermeable geologic formations. An artesian well is free flowing.




Link to the definition of Backflow

A reverse flow condition, created by a difference in water pressures, which causes water to flow back into the distribution pipes of a potable water supply from any source or sources other than an intended source. Also see backsiphonage and cross-connection.

Bay Delta 

Link to the definition of Bay Delta

The San Francisco Bay/San Joaquin Delta is an estuary forming 700 miles of waterways, surrounding 57 islands. The State Water Project and Central Valley Project extract water from the Bay-Delta for delivery south.

Best management practices (BMPs) 

Link to the definition of Best management practices (BMPs)

Structural, nonstructural and managerial techniques that are recognized to be the most effective and practical means to control nonpoint source pollutants yet are compatible with the productive use of the resource to which they are applied. BMPs are used in both urban and agricultural areas.

Brackish Water 

Link to the definition of Brackish Water

Mixed fresh and salt waters.

Brown Act 

Link to the definition of Brown Act

Ralph M. Brown Act enacted by the State legislature governing all meetings of legislative bodies. Also know as the Open Meeting requirements.



Capital costs 

Link to the definition of 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.

Central Valley Project 

Link to the definition of Central Valley Project

Federally owned aqueduct carrying water from Northern California to regions in Los Angeles.


Link to the definition of Chloramines

Compounds formed by the reaction of hypochlorous acid (or aqueous chlorine) with ammonia.


Link to the definition of Chlorination

The application of chlorine to water, generally for the purpose of disinfection, but frequently for accomplishing other biological or chemical result (aiding coagulation and controlling tastes and odors).

Chlorine demand 

Link to the definition of Chlorine demand

Chlorine demand is the difference between the amount of chlorine added to water and the amount of residual chlorine remaining after a given contact time. Chlorine demand may change with dosage, time, temperature, pH, and nature and amount of the impurities in the water.

Clear Well 

Link to the definition of Clear Well

A reservoir for the storage of filtered water of sufficient capacity to prevent the need to vary the filtration rate with variations in demand. Also used to provide chlorine contact time for disinfection.


Link to the definition of Coagulation

The clumping together of very fine particles into larger particles caused by the use of chemicals (coagulants). The chemicals neutralize the electrical charges of the fine particles. This clumping together makes it easier to separate the solids from the water by settling, skimming, draining, or filtering.


Link to the definition of Coliform

A group of bacteria found in the intestines of warm-blooded animals (including humans) and also in plants, soil, air and water. Fecal coliforms are a specific class of bacteria, which only inhibit the intestines of warm-blooded animals. The presence of coliform bacteria is an indication that the water is polluted and may contain pathogenic organisms.

Colorado River 

Link to the definition of Colorado River

One of Metropolitan Water District of Southern California's import water sources, supplying water and hydroelectric power for Southern Californians. Supplies about 65 percent of total water used south of the Tehachapi Mountains, from the Pacific Ocean to the river.


Link to the definition of Conductance

A rapid method of estimating the dissolved-solids content of a water supply. The measurement indicates the capacity of a sample of water to carry an electrical current, which is related to the concentration of ionized substances in the water. Also called Specific Conductance.

Conjunctive use 

Link to the definition of Conjunctive use

The planned use of groundwater in conjunction with surface water in overall management to optimize total water resources.

Continuous sample 

Link to the definition of Continuous sample

A flow of water from a particular place in a water treatment plant to the location where samples are collected for testing. This continuous stream may be used to obtain grab or composite samples. Frequently, several taps (faucets) will flow continuously in the laboratory to provide test samples from various places in a water treatment plant.


Link to the definition of Corrosivity

An indication of the corrosiveness of water. The water’s pH, alkalinity, hardness, temperature, total dissolved solids, dissolved oxygen concentration, and the Langelier Index describe the corrosiveness of water.

Cost/benefit analysis 

Link to the definition of Cost/benefit analysis

A quantitative evaluation of the costs that would be incurred versus the overall benefits to society of a proposed action such as the establishment of an acceptable dose of a toxic chemical.


Link to the definition of Cross-connection

Any actual or potential connection between a drinking (potable) water system and an unapproved water supply or other source of contamination. For example, if you have a pump moving nonpotable water and hook into the drinking water system to supply water for the pump seal, a cross-connection or mixing between the two water systems can occur. This mixing may lead to contamination of the drinking water.

Curb stop 

Link to the definition of Curb stop

A water service shutoff valve located in a water service pipe near the curb and between the water main and the building. This valve is usually operated by a wrench or valve key and is used to start or stop flows in the water service line to a building. Also called a "curb cock."




Link to the definition of Demineralization

A treatment process that removes dissolved minerals (salts) from water.


Link to the definition of Desalinization

The removal of dissolved salts (such as sodium chloride, NaCl) from water by natural means (leaching) or by specific water treatment processes.

Direct filtration 

Link to the definition of Direct filtration

A filtration method of treating water which consists of the addition of coagulant chemicals, flash mixing, coagulation, minimal flocculation, and filtration. The flocculation facilities may be omitted, but the physical-chemical reactions will occur to some extent. The sedimentation process is omitted.


Link to the definition of Disinfection

The process designed to kill most microorganisms in water, including essentially all pathogenic (disease-causing) bacteria. There are several ways to disinfect, with chlorine being most frequently used in water treatment. Compare with sterilization.

Disinfection by-product 

Link to the definition of Disinfection by-product

A compound formed by the reaction of a disinfectant such as chlorine with organic material in the water supply.




Link to the definition of E.P.A.

United States Environmental Protection Agency.


Link to the definition of Effluent

Water or some other liquid (raw, partially or completely treated) flowing from a reservoir, basin, treatment process or treatment plant.


Link to the definition of Estuary

Area where tidal and river currents meet, and where salinity is between the extremes of ocean and fresh waters.


Link to the definition of 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.


Link to the definition of Evapotranspiration

The combined processes of evaporation and transpiration. It can be defined as the sum of water used by vegetation and water lost by evaporation.




Link to the definition of Filtration

A process for removing particulate matter from water by passage through porous media.

Finished water 

Link to the definition of Finished water

Water that has passed through a water treatment plant. All the treatment processes are completed or "finished". This water is ready to be delivered to consumers. Also called Product Water.

First draw 

Link to the definition of First draw

The water that immediately comes out when a tap is first opened. This water is likely to have the highest level of lead contamination from plumbing materials.

First draw sample 

Link to the definition of First draw sample

A one-liter sample of tap water that has been standing in plumbing pipes at least six hours, and is collected without flushing the tap.


Link to the definition of Floc

Clumps of bacteria and particulate impurities that have come together and formed a cluster. Found in flocculation tanks and settling or sedimentation basins.


Link to the definition of Flocculation

The gathering together of fine particles in water by gentle mixing after the addition of coagulant chemicals to form larger particles.


Link to the definition of Fluoridation

The addition of a chemical to increase the concentration of fluoride ions in drinking water, to a predetermined optimum limit, to reduce the incidence (number) of dental caries (tooth decay) in children. Defluoridation is the removal of excess fluoride in drinking water to prevent the mottling (brown stains) of teeth.


Link to the definition of 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.

Fresh water 

Link to the definition of Fresh water

Water that generally contains less than 1,000 milligrams-per-liter of dissolved solids.



Giardia Lamblia 

Link to the definition of Giardia Lamblia

Flagellate protozoan which is shed during its cyst stage into the feces of humans and animals. When water containing these cysts is ingested, the protozoan causes a severe gastrointestinal disease called giardiasis.


Link to the definition of Giardiasis

Intestinal disease caused by an infestation of Giardia flagellates.

Green Acres Project (GAP) 

Link to the definition of Green Acres Project (GAP)

A 7.5 million gallons per day (Mgd) water reclamation project that serves tertiary treated recycled water to irrigation and industrial users in Costa Mesa, Fountain Valley, Huntington Beach, Newport Beach, and Santa Ana.

Grey water 

Link to the definition of Grey water

Wastewater other than sewage, such as sink drainage or washing machine discharge.


Link to the definition of Groundwater

The supply of fresh water found beneath the Earth's surface, usually in aquifers, which is often used for supplying wells and springs. Because groundwater is a major source of drinking water, there is growing concern over areas where leaching agricultural or industrial pollutants or substances from leaking underground storage tanks are contaminating groundwater.

Groundwater basin 

Link to the definition of Groundwater basin

A groundwater reservoir defined by all the overlying land surface and the underlying aquifers that contain water stored in the reservoir. Boundaries of successively deeper aquifers may differ and make it difficult to define the limits of the basin.



Hard water 

Link to the definition of Hard water

Alkaline water containing dissolved salts that interfere with some industrial processes and prevent soap from lathering. Water may be considered hard if it has a hardness greater than the typical hardness of water from the region. Some textbooks define hard water as water with a hardness of more than 100 mg/L as calcium carbonate.

Hardness, water 

Link to the definition of Hardness, water

A characteristic of water caused mainly by the salts of calcium and magnesium, such as bicarbonate, carbonate, sulfate, chloride and nitrate. Excessive hardness in water is undesirable because it causes the formation of soap curds, increased use of soap, deposition of scale in boilers, damage in some industrial processes, and sometimes causes objectionable tastes in drinking water.

Hydrogeologic cycle 

Link to the definition of Hydrogeologic cycle

The natural process recycling water from the atmosphere down to (and through) the earth and back to the atmosphere again.



Import Water 

Link to the definition of Import Water

Water purchased from the Metropolitan Water District of Southern California through Municipal Water District of Orange County. Import water comes from two sources, the Colorado River and the State Water Project.


Link to the definition of Influent

Wastewater entering a treatment plant.



Maximum contaminant level (MCL) 

Link to the definition of Maximum contaminant level (MCL)

The maximum permissible level of a contaminant in water which is delivered to the free flowing outlet of the ultimate user of a public water system, except in the case of turbidity where the maximum permissible level is measured at the point of entry to the distribution system. Contaminants added to the water under circumstances controlled by the user are excluded from this definition, except those contaminants resulting from the corrosion of piping and plumbing caused by water quality.

Mesa Water 

Link to the definition of Mesa Water

Mesa Water District. A retail water agency serving the city of Costa Mesa, parts of Newport Beach and parts of unincorporated Orange County, including the John Wayne Airport.


Link to the definition of MGD

Million gallons per day.

Monitoring wells 

Link to the definition of Monitoring wells

Wells used to collect groundwater samples for analysis to determine the amount, type, and spread of contaminants in groundwater.


Link to the definition of MWD

Metropolitan Water District of Southern California was created by founding-area voters in 1928, following passage of an enabling bill by the California Legislature, to provide supplemental water for cities and communities on the south coastal plain. Metropolitan Water District's service area now includes about 225 cities and unincorporated areas, and covers some 5,200 square miles in Los Angeles, Orange, San Diego, Riverside, San Bernardino and Ventura counties.


Link to the definition of MWDOC

Municipal Water District of Orange County, a wholesale water agency, sells import water from Metropolitan Water District to retail water agencies throughout Orange County.




Link to the definition of Nitrification

The biochemical transformation of ammonium nitrogen to nitrate nitrogen.


Link to the definition of Non-potable

Water that may contain objectionable pollution, contamination, minerals, or infective agents and is considered unsafe and/or unpalatable for drinking.




Link to the definition of OCWD

Orange County Water District. Agency charged with managing the Orange County Groundwater Basin.

Odor threshold 

Link to the definition of Odor threshold

The minimum odor of a water sample that can just be detected after successive dilutions with odorless water. Also called Threshold Odor.

Operation and maintenance costs 

Link to the definition of Operation and maintenance costs

The ongoing, repetitive costs of operating a water system; for example, planned maintenance and costs for treatment chemicals, and periodic equipment repairs.

Orange County Groundwater Basin 

Link to the definition of Orange County Groundwater Basin

The basin where groundwater and rain runoff is naturally stored.


Link to the definition of Ozonation

The application of ozone to water for disinfection or for taste and odor control.



Parts per million 

Link to the definition of Parts per million

Parts per million, a measurement of concentration on a weight or volume basis. This term is equivalent to milligrams per liter (mg/L) which is the preferred term.


Link to the definition of Percolation

The slow seepage of water into and through the ground. The slow passage of water through a filter medium.


Link to the definition of Permeability

Generally used to refer to the ability of rock or soil to transmit water.


Link to the definition of pH

pH is an expression of the intensity of the basic or acid condition of a liquid. Mathematically, pH is the logarithm (base 10) of the reciprocal of the hydrogen ion concentration, [H+].


Link to the definition of Picocurie

A measure of radioactivity. One picocurie of radioactivity is equivalent to 0.037 nuclear disintegrations per second.

Point-of-use treatment device 

Link to the definition of Point-of-use treatment device

A treatment device applied to a single tap used for the purpose of reducing contaminants in drinking water at that one tap.


Link to the definition of 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.

Potable water 

Link to the definition of Potable water

Water that is safe and satisfactory for drinking and cooking.


Link to the definition of ppb

Parts per billion.


Link to the definition of ppm

Parts per million. Also mg/L or milligrams per liter.

Product water 

Link to the definition of Product water

Water that has passed through a water treatment plant. All the treatment processes are completed or finished. This water is the product from the water treatment plant and is ready to be delivered to the consumers. Also called finished water.


Link to the definition of psi

Pounds per square inch.

Pumping station 

Link to the definition of Pumping station

Mechanical devices installed in sewer or water systems or other liquid-carrying pipelines that move the liquids to a higher level.

Purveyor, water 

Link to the definition of Purveyor, water

An agency or person that supplies water (usually potable water).



Raw water 

Link to the definition of Raw water

Water in its natural state, prior to any treatment. Usually the water entering the first treatment process of a water treatment plant.


Link to the definition of Recharge

Process by which rainwater (precipitation) seeps into the ground-water system.

Recharge area 

Link to the definition of Recharge area

Generally, an area that is connected with the underground aquifer(s) by a highly porous soil or rock layer. Water entering a recharge area may travel for miles underground.

Recharge rate 

Link to the definition of Recharge rate

The quantity of water per unit time that replenishes or refills an aquifer.

Reclaimed Water 

Link to the definition of Reclaimed Water

Highly treated wastewater. California has one of the most stringent wastewater reclamation criteria in the U.S. Reclaimed water treatment steps:

  1. Primary Treatment - Sand, grit and the larger solids are separated from the liquid, removing 45 to 50 percent of the waste materials. The residual water, or effluent, can be used for irrigating orchards and vineyards, and animal feed, fiber and seed crops. Opportunities for using this type of reclaimed water do not exist in Los Angeles.
  2. Secondary Treatment - This step, largely a biological process, removes 85 percent of the remaining waste materials. Bacteria and other organisms consume these materials. The wastewater is then disinfected to kill any remaining harmful bacteria. The reclaimed water produced at this stage is 95 percent free of the original solids and organic matter. It can be used for surface irrigation (flooding) of most crops, pastures, cemeteries, and other large turf areas.
  3. Tertiary Treatment - This advanced step filters and removes nearly all remaining fine solids. Water is chlorinated for disinfection, then dechlorinated to protect fish and other aquatic life. Reclaimed tertiary effluent can be used for irrigation of parks and playgrounds, spray irrigation of food crops, and some types of groundwater recharge.

Representative sample 

Link to the definition of Representative sample

A portion of material or water that is as nearly identical in content and consistency as possible to that in the larger body of material or water being sampled.


Link to the definition of Reservoir

Any natural or artificial holding area used to store, regulate, or control water.

Residual chlorine 

Link to the definition of Residual chlorine

The amount of free and/or available chlorine remaining after a given contact time under specified conditions.

Reverse osmosis 

Link to the definition of Reverse osmosis

The application of pressure to a concentrated solution, which causes the passage of a liquid from the concentrated solution to a weaker solution across a semipermeable membrane. The membrane allows the passage of the solvent (water) but not the dissolved solids (solutes). The liquid produced is a demineralized water

Riparian rights 

Link to the definition of Riparian rights

A doctrine of State water law under which a land owner is entitled to use the water on or bordering his property, including the right to prevent diversion or misuse of upstream waters. Riparian land is land that borders on surface water.


Link to the definition of Run-off

The part of precipitation, snowmelt, or irrigation water that runs off the land into streams or other surface water. It can carry pollutants from the air and land into the receiving waters.



Safe Drinking Water Act (SDWA) 

Link to the definition of Safe Drinking Water Act (SDWA)

An Act passed by the U.S. Congress in 1974. The Act establishes a cooperative program among local, State and Federal agencies to insure safe drinking water for consumers.


Link to the definition of Salinity

The relative concentration of dissolved salts, usually sodium chloride, in a given water. A measure of the concentration of dissolved mineral substances in water.


Link to the definition of Sedimentation

A water treatment process in which solid particles settle out of the water being treated in a large clarifier or sedimentation basin.


Link to the definition of Seepage

The percolation of water through the soil from unlined channels, ditches, watercourses and water storage facilities.


Link to the definition of Sludge

The settable solids separated from water during processing.


Link to the definition of Slurry

A watery mixture or suspension of insoluble (not dissolved) matter, a thin watery mud or any substance resembling it (such as a grit slurry or a lime slurry).


Link to the definition of SMCLs

Secondary Maximum Contaminant Levels. Secondary MCLs for various water quality indicators are established to protect public welfare.

Soil profile 

Link to the definition of Soil profile

A vertical section of the earth's highly weathered upper surface often showing several distinct layers, or horizons.

Sole source aquifer 

Link to the definition of Sole source aquifer

An aquifer that supplies 50 percent or more of the drinking water of an area.


Link to the definition of Standard

A physical or chemical quantity whose value is known exactly, and is used to calibrate or standardize instruments.


Link to the definition of Sterilization

The removal or destruction of all microorganisms, including pathogenic and other bacteria, vegetative forms and spores. Compare with disinfection.

Surface runoff 

Link to the definition of Surface runoff

Precipitation, snowmelt, or irrigation in excess of what can infiltrate the soil surface and can be stored in small surface depressions. Runoff is a major transporter of nonpoint source pollutants.

Surface water 

Link to the definition of Surface water

All water naturally open to the atmosphere (rivers, lakes, reservoirs, streams, impoundments, seas, estuaries, etc.); and all springs, wells, or other collectors which
are directly influenced by surface water.

Suspended solids 

Link to the definition of Suspended solids

Solids that either float on the surface or are suspended in water or other liquids, and which are largely removable by laboratory filtering. The quantity of material removed from water in a laboratory test, as prescribed in “Standard Methods for The Examination of Water and Wastewater”.




Link to the definition of Telemetry

The electrical link between the transmitter and the receiver. Telephone lines are commonly used to serve as the electrical line.

Total dissolved solids (TDS) 

Link to the definition of Total dissolved solids (TDS)

All of the dissolved solid in a water. TDS is measured on a sample of water that has passed through a very fine mesh filter to remove suspended solids. The water passing through the filter is evaporated and the residue represents the dissolved solids.

Total residual chlorine 

Link to the definition of Total residual chlorine

The amount of available chlorine remaining after a given contact time. The sum of the combined available residual chlorine and the free available residual chlorine.

Total trihalomethanes (TTHMs) 

Link to the definition of Total trihalomethanes (TTHMs)

The sum of the concentration, in milligrams per liter, of the several trihalomethane compounds, rounded to two significant figures.

Treated wastewater 

Link to the definition of Treated wastewater

Wastewater that has been subjected to one or more physical, chemical, and biological processes to reduce its pollution of health hazard.

Trihalomethane (THM) 

Link to the definition of Trihalomethane (THM)

One of a family of organic compounds, named as derivatives of methane. THMs are generally the by-product from chlorination of drinking water that contains organic material. The resulting compounds (THMs) are suspected of causing cancer.


Link to the definition of Turbidity

The cloudy appearance of water caused by the presence of suspended and colloidal matter. In the waterworks field, a turbidity measurement is used to indicate the clarity of water.

Technically, turbidity is an optical property of the water based on the amount of light reflected by suspended particles. Turbidity cannot be directly equated to suspended solids because white particles reflect more light than dark-colored particles and many small particles will reflect more light than an equivalent large particle.



Ultraviolet light disinfection 

Link to the definition of Ultraviolet light disinfection

A disinfection method for water that has received either secondary or tertiary treatment, used as an alternative to chlorination.

User fee 

Link to the definition of User fee

A fee that is collected only from those persons who use a particular service as opposed to one collected from the public in general. User fees generally vary in proportion to the degree of use of the service.



Variable costs 

Link to the definition of Variable costs

Input costs that change as the nature of the production activity of its circumstances change. For example, as production levels vary.




Link to the definition of Wastewater

The used water and solids from a community (including used water from industrial processes) that flow to a treatment plant. Storm water, surface water, and groundwater infiltration also may be included in the wastewater that enters a wastewater treatment plant. The term -sewage usually refers to household wastes, but this word is being replaced by the term -wastewater.

Wastewater treatment plant 

Link to the definition of Wastewater treatment plant

A facility that receives wastewaters (and sometimes runoff) from domestic and/or industrial sources; and by a combination of physical, chemical, and biological processes reduces (treats) the wastewaters to less harmful byproducts known by the acronyms WWTP, STP (sewage treatment plant) and POTW (publicly owned treatment works).

Water purveyor 

Link to the definition of Water purveyor

An agency or person that supplies water (usually potable water).

Water table 

Link to the definition of Water table

The level of groundwater. The upper surface of the zone of saturation of groundwater above an impermeable layer of soil or rock (through which water cannot move) as in an unconfined aquifer. This level can be very near the surface of the ground or far below it.

Waterborne disease outbreak 

Link to the definition of 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.


Link to the definition of Watershed

The land area that drains into a stream. An area of land that contributes runoff to one specific delivery point. Large watersheds may be composed of several smaller "subsheds", each of which contributes runoff to different locations that ultimately combine at a common delivery point.


Link to the definition of 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 field 

Link to the definition of Well field

Area containing one or more wells that produces usable amounts of water.

Well monitoring 

Link to the definition of Well monitoring

The measurement, by on-site instruments or laboratory methods, of the quality of water in a well.

Well plug 

Link to the definition of Well plug

A watertight and gastight seal installed in a borehole or well to prevent movement of fluids.


Link to the definition of Wetlands

Any number of tidal and nontidal areas, characterized by saturated or nearly saturated soils most of the year, which form an interface between terrestrial (land-based) and aquatic environments. Includes freshwater marshes around ponds, channels, rivers and streams, and brackish and salt marshes. Other common names include swamps and bogs.


Link to the definition of Withdrawal

The process of taking water from a source and conveying it to a place for a particular type of use.