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Below is a listing of commonly used terms in the water industry, divided into categories. We also offer two pdf documents with a compiled list of glossary terms for low and upper grades.

Different Types of Water 


Wastewater that contains animal, human or food wastes.


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

Brackish Water

A mixture of freshwater and saltwater.


Water segregated from a domestic wastewater collection system and reused on site. This water can come from a variety of sources such as showers, bathtubs, washing machines, and bathroom sinks. It contains some soap and detergent, but is clean enough for non-potable uses. Water from toilets or wash water from diapers is not considered to be greywater. Kitchen sink water is not considered greywater in many states. Many buildings or individual dwellings have systems that capture, treat and distribute greywater for irrigation or other non-potable uses.

Potable water

Drinking water that meets or exceeds state and federal drinking standards.

Reclaimed water

Previously used water that has been treated for reuse but has not yet been put to another use. Once reclaimed water is put to some purpose it is referred to as recycled or reused water.

Recycled water

Water that is used more than once and has been treated to a level that allows for its reuse for a beneficial purpose.


The used water of a household and commercial businesses that contains human waste. The term sewage is distinguished from industrial wastewater. The term sewage can be used interchangeably with wastewater.


The used water of a community or industry that contains dissolved or suspended matter. Types of wastewater include domestic wastewater/sewage from household uses and industrial/commercial wastewater generated by industries, small businesses and commercial enterprises.

Water and Groundwater Basics 

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.


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


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

Capillary Action

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 through the pore spaces.


Process by which water vapor changes to a liquid. Condensation is a key part of the water cycle because it is responsible for the formation of clouds. Cloud formation occurs around condensation surfaces such as small particles of matter (dust and salt) suspended in the atmosphere


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.


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

Cubic foot

Measurement of a volume of water, used frequently in the water industry. One cubic foot (cf) equals 7.48 gallons.

Confined Aquifer

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

Cubic Feet Per Second (CFS)

A measure of volume of water flow per time (also known as discharge) of water through a stream or pipe. A cubic foot per second is 450 gallons per minute.


A prolonged period of below-average precipitation.


The processes of picking up and moving sediments or rocks by various agents including streams, glaciers, wind, and gravity. This process changes the shape of the land surface and is active in some form across the globe.


Water changing into vapor and rising into the air.


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.

Groundwater Recharge or Replenishment

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


Million acre-feet. Commonly used to describe large amounts of water in the industry.


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

Water Cycle

Describes how water moves on the Earth. Water evaporates from water bodies (such as oceans, lakes, and rivers), forms clouds, and returns to earth as precipitation (rain or snow). The amount of water that evaporates each year and the amount that falls back to the ground are virtually constant, meaning that the amount of water on Earth does not change. Water reuse solutions essentially use technology to mimic the natural cycle and create clean water – faster and more efficiently – than it would otherwise be available.

Water Production, Treatment and Transport 

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.

Advanced purified water or purified water

Water that has passed through proven treatment processes and has been verified through monitoring to be safe for augmenting drinking water supplies. The source water for advanced treatment is often clean water from a wastewater treatment or resource recovery plant. Purification processes can involve a multistage process such as microfiltration, reverse osmosis and advanced oxidation, as well as Soil Aquifer Treatment. Any of these options are capable of producing water quality that has been verified through monitoring to be safe for augmenting drinking water supplies


Man-made canal or pipeline used to transport water.


Man-made canal or pipeline used to transport water.


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.

Central Valley Project (CVP)

A series of dams, reservoirs and canals in the San Joaquin Valley of California.

Colorado River Aqueduct (CRA)

Built 1933-1941 and owned and operated by the Metropolitan Water District of Southern California.

Combined Sewers

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

Conjunctive Use

Storing imported water in a local aquifer, in conjunction with groundwater, for later retrieval and use. Conjunctive use means actively managing the aquifer systems as an underground reservoir. During wet years, when more surface water is available, surface water is stored underground by recharging the aquifers with surplus surface water.

Diamond Valley Lake (DVL)

Metropolitan’s major reservoir near Hemet, in southwestern Riverside County.

Title 22 Standards

Requirements established by the California Department of Health Services (now the State Water Resources Control Board) for the production

Tertiary treatment or advanced water treatment

Processes that purify water for uses such as irrigation or for water blended with other environmental systems such as a river, reservoir, or groundwater basin prior to reuse. It can also include treatment processes to remove nitrogen and phosphorus in order to allow discharge into a highly sensitive or fragile ecosystem (estuaries, low-flow-rivers, coral reefs, etc.).

Secondary treatment

Process where dissolved and suspended biological matter is removed to a non-potable level so that the water may be disinfected and discharged into a stream or river, or used for irrigation at controlled locations.

Primary treatment

Process where solid matter is removed. The remaining liquid may be discharged or subjected to further treatment.

Million gallons per day (MGD)

A measure of volume of water per time. Commonly used for water treatment plants and other facilities’ production and/or pumping.

Hydroelectric Plant

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


Water flowing from a structure such as a treatment plant. (Contrast with influent)

Water Policies and Regulations 

Sustainable Groundwater Management Act of 2014

California enacted landmark legislation in 2014 known as the Sustainable Groundwater Management Act (SGMA). The legislation provides a framework for sustainable management of groundwater supplies by local authorities, with a limited role for state intervention only if necessary to protect the resource.

Environmental Impact Report (EIR)

A state-mandated written summary of the positive and negative effects on the environment caused by the construction and operation of a project.

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.

California Environmental Quality Act (CEQA)

Requires an assessment of the possible environmental impacts of projects.


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.


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

Water Agencies and Governing Bodies 

California Urban Water Conservation Council (CUWCC)

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

California Department of Water Resources (DWR)

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

California Urban Water Agencies (CUWA)

Group of 11 member agencies serving two-thirds of state's population.

County Water Authority

A public water district serving a county-wide area.

Municipal Water District

A public water provider governed by a locally elected board of directors, which supplies water to the public directly or through sub agencies.

Municipal Water Quality Investigation (MWQI)

Section of the CA Department of Water Resources that monitors water quality in the Delta for drinking water purposes. Water quality samples and studies are performed throughout the Sacramento watershed, the Sacramento-San Joaquin Delta, and the San Francisco Bay Area.

Water Quality and Monitoring/Mitigation 


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.


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


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.


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.


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.


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


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.


A test for a particular chemical or effect. 

Bacteria (Plural) / Bacterium (Singular)

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


A 10- to 20-foot-long pipe equipped with a valve at the lower end. Used to retrieve groundwater samples from monitoring wells.


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


A covered hole or pit for receiving sewage.

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.


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


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

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).


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.


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


An agent that destroys or inactivates harmful microorganisms.


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.


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.

Color (of water)

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.

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.


Passing water through coal, sand and gravel to remove particles.


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


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

Fluoride Ion (F-)

A halide ion. Fluoride salts are added to drinking water for fluoridation. Fluoride is regulated by the US Environmental Protection Agency.


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.


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


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

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.


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


An organism of microscopic size, such as bacterium.


Relating to microorganisms and their life processes.

Maximum Contaminant Level (MCL)

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.

Nonpoint Source Pollution

Pollution which comes from diffuse sources such as urban and agricultural runoff. Non-point source pollution is often difficult to identify and to treat.

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.

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.

Water Use and Conservation 

Beneficial Reuse

The use of recycled water for purposes that contribute to the water needs, economy and/or environment of a community.

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.

De-facto, Unacknowledged or Unplanned Potable Reuse

When water intakes draw raw water supplies downstream from discharges of clean water from wastewater treatment plants, water reclamation facilities, or resource recovery facilities. For example, if you are downstream of a community, that community’s used water gets put back into a river or stream and is delivered downstream to your community and after further treatment becomes part of your drinking water supply.

Direct Potable Reuse (DPR)

Involves putting recycled water directly into a potable water supply distribution system downstream of a water treatment plant or into the source water supply immediately upstream of the water treatment plant

Direct or indirect potable reuse

Commonly involves a more formal public process and public consultation program than is observed with de-facto or unacknowledged reuse.

Endangered Species

A species of animal or plant threatened with extinction. 


A program to reduce agricultural water use 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. 

Indirect Potable Reuse (IPR)

involves blending recycled water with other environmental systems such as a river, reservoir or groundwater basin, before the water is reused for drinking water.

Integrated Resources Plan (IRP)

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.


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

Non-potable Reuse

The use of recycled water for purposes other than drinking purposes, such as irrigation and industrial uses.

Planned Potable Reuse

An intentional project to use recycled water for drinking water. It is sometimes further defined as either:

Potable Reuse

The use of recycled water for drinking water purposes. The water is purified sufficiently to meet or exceed federal and state drinking water standards and is safe for human consumption.

Water Conservation Video Glossary 


Amphibians are cold-blooded animals with backbones; the adults breathe air with their lungs, and can also breathe through their moist skin. Amphibians, such as frogs or toads, live on land and in water. When reproducing, amphibians lay their eggs in water. The eggs hatch into gill-breathing larval – like tadpoles, and later develop into adults with lungs.


Plants and animals that live near or in the water most or all of their lives.


A large area of water that is partially surrounded by land but opens to an ocean or lake. San Francisco Bay is a body of water with an opening that leads to the Pacific Ocean. (see estuary)


A pure substance or a product which is often prepared or created by humans. Many chemicals can hurt the environment or people if they are inhaled, eaten, or absorbed through the skin.


The long-term weather patterns in a place or region.


A chemical that is often added to water to kill bacteria, but may also harm wildlife.


The area where rivers meet and join, or where one major river begins to ‘spit off’. In California, the largest is the Sacramento-San Joaquin Delta, where the Sacramento and San Joaquin Rivers meet to drain into the San Francisco Bay. This region includes many kinds of habitats—riparian, marsh, river, agricultural lands, grassland, and estuary.


A wall that is built across a river or stream to slow the natural flow of water. Dams serve to control floods, store water for people, and often produce hydroelectric energy.


The careful use of natural resources (such as trees, oil, and water) to prevent them from being wasted, depleted, or damaged.


A decaying and rotting mixture of plants or plant food leftovers (such as leaves, grass, fruit, vegetables etc.) that is used in the garden to improve soil health and promote the growth of plants.


A group of plants and animals that live in the same area and interact with each other.


An illness which impacts people, plants, or animals.


A pipe that carries water and liquid waste away from buildings and streets.

Drip tubing

A method of watering plants that saves water. A small hose or tube is laid on the ground or buried just under the surface of the soil. The tube has small holes in it, allowing water to drip out slowly.


A long period of time during which an area that usually has precipitation gets very little to no rain, or snow.


A form of energy that is carried through wires and is used to operate machines, lights, appliances, etc. Electricity has many sources.


An area where a river flows into the sea and there is a mixing of salt water and freshwater. Estuaries are important habitat for fish, birds, and other animals.


Water dries up when the sun heats it and turns it into vapor or steam. The water vapor or steam leaves the river, lake, ocean, or land, and rises into the atmosphere.

Food Chain

Food energy is transferred from one living thing to another. Every organism can be thought of as a link in a chain. For example, insects eat plants, salmon eats insects, and otters eat salmon.


Consists of small rocks. The life-cycle of a salmon begins when eggs are laid in the gravel habitat along river or stream banks. When the eggs hatch, the alevin stage of the salmon develops in the gravel, growing into small fish which then leave the gravel to feed on plankton in the rivers.


Water within the earth that supplies wells and springs.Geological formations called aquifers hold and contain groundwater.


The place where an animal lives. A habitat provides the animal with food, water, shelter, and space. There are many different types of habitats around the world, including rivers, forests, grasslands, mountains, and deserts. Different habitats are home to different animals.


Energy that comes from the force of moving water, usually from a dam. The word "hydro" means water.


Man-made ways of taking water from its source to an area that would normally be dry. For example, sprinklers and hoses are ways to irrigate a farm or garden.


A particular way of living, the way a person lives or a group of people live.


A major change in the form or structure of all insects and some animals, which happens as the insect or animal becomes an adult. For example, when a frog hatches from its egg it is a tadpole, but later it changes into a frog.


To travel a large distance from one area or region to another at different times of the year.


A material made from various organic ingredients such as leaves, bark, or compost. Mulch is spread around or over plants to enrich, insulate, and protect the soil and plants. Mulch is also used to limit the amount of evaporation that happens. Mulch allows the plants and soil to stay cool and moist.


Refers to animals or plants that naturally occur in an area.

Native plants

Plants that have always lived here rather than those brought here by humans. Over time, native plants have adapted to the local temperatures, water availability, and soil types (among other things.)


A non-native organism is one that has been introduced or brought into a new area to live by people.


Animals that are not tamed or domesticated, including, but not limited to: insects, spiders, birds, reptiles, fish, amphibians, and mammals.


The land area from which surface runoff drains into stream channel, lake, reservoir, or other body of water; also called a drainage basin.

Water Cycle

The continuous circulation of water in systems throughout the planet, involving condensation, precipitation, runoff, evaporation, and transpiration.

Water Conservation

The use of water-saving methods to reduce the amount of water needed for homes, lawns, farming, and industry. By conserving water people can save money, live better, and help the natural world.


An engine with large blades that spin when water flows through them. At dams, they transform the energy from the water to electricity and provide energy for houses, hospitals, and schools. Windmills are another kind of turbine that captures the energy from the wind.

Storm drain

A system of large pipes designed to drain extra rain and surface water from paved streets, parking lots, sidewalks, and roofs. There is often a grate on the street that covers the drain pipe. Storm drains usually lead to creeks or rivers.


A population of individuals that are more or less alike and are able to breed and produce fertile offspring under natural conditions.


The process where some aquatic animals release and deposit sperm and eggs into the water for reproduction.


Melting snow produces water that flows over the surface of the ground into streams and rivers.


The nozzle that sprays water on you when you are in the shower. A low flow showerhead decreases the amount of water that comes out so you use less.


Material such as stones, soil, and sand that is carried into water by wind or water. The “dirt” that falls to the bottom of the river is called, “sediment.”


A large fish that is hatched in streams or rivers, but lives most of its life in the ocean, before returning to spawn in rivers.


Water that drains or flows off the surface of the land (including streets).


The community or habitat of plants living along or near a stream, river, or body of water. It is usually a type of woodland habitat.


Cold-blooded, air-breathing vertebrates having skin covered with scales or bony plates, true claws (if they have legs), and lay soft-shelled leathery eggs. Most common examples are tortoises, turtles, lizards, snakes, alligators, and crocodiles.


Animals that are killed and eaten by other animals.


An animal that kills and eats other animals.


A gaseous element that is found in the air. It has no color, taste, or smell, and it is a main building block for life on Earth. Sometimes oxygen is used as another word for “air.”


A living thing such as an animal, plant, fungus, or bacteria.