Any substance that has a pH level below 7, or that has more free hydrogen ions (H+) than hydroxide ions (OH).


The amount or degree to which a substance is an acid.

Acre Foot (AF)

An acre-foot is a unit of volume commonly used in the United States in reference to large-scale water resources, such as reservoirs, aqueducts, canals, sewer flow capacity, and river flows. One acre-foot is equivalent to 325,900 gallons.


The attraction of water molecules to other materials as a result of hydrogen bonding.


Able to live only in the presence of air or free oxygen; conditions that exist only in the presence of air or free oxygen.


Organisms that are closely related to higher plants that perform photosynthesis and are commonly found in or near water, such as seaweed and pond scum.


Able to live and grow only where there is no air or free oxygen; conditions that exist only in the absence of air and free oxygen.


An artificial channel for conveying water, typically in the form of a bridge across a valley or other gap.


An underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand or silt) from which groundwater can be extracted using a water well.


Excessively dry or without moisture


The layer of gases surrounding Earth; composed mainly of nitrogen and oxygen.


A flow of a liquid opposite to the usual or desired direction.


Single-celled microorganisms that are either free-living or grow on and derive nourishment from dead or decaying organic matter. Some bacteria cause disease in plants and animals.


Any substance that has a pH level above 7, or that has more free hydroxide ions (OH) than hydrogen ions (H+).


A large or small depression in the surface of the land or on the ocean floor. A geographical feature describing a depression or lower lying area than the surrounding terrain.


Nutrient-rich organic materials obtained from wastewater treatment and used beneficially as a fertilizer.


Best Management Practice.


A very common non-metal element that is the foundation for life on Earth.

Carbon Dioxide (C02)

A heavy, colorless, gaseous compound comprised of one Carbon atom and two Oxygen atoms. It comprises about 0.039% of the Earth’s atmosphere and is considered a greenhouse gas affecting the Earth’s climate.

Catch Basin

A reservoir, well or low area where surface water may drain into.


To combine or treat with chlorine.


A strong-smelling, poisonous, gaseous element that occurs in nature usually combined with other elements, such as sodium (Na) to form salt (NaCl). In its purer form, it is used as an anti-bacterial/fungal cleaning agent.

Clean Water Act (CWA)

The primary federal law in the United States governing water pollution.


The action or process of a liquid, especially blood, changing to a solid or semi-solid state.


The attraction of water molecules to each other as a result of hydrogen bonding.

Colorado River Aqueduct

The Colorado River Aqueduct, or CRA, is a 242 mi water conveyance in Southern California in the United States, operated by the Metropolitan Water District of Southern California

Common-Law Doctrine (aka Riparian Rights)

A legal doctrine used in many states east of the Mississippi that states a property owner has the right to use any water that exists on or crosses their property.


Decayed organic matter often found in topsoil.


The process by which a vapor becomes a liquid; the opposite of evaporation.

Confined Aquifer

A water-saturated layer of soil or rock that is bounded above and below by impermeable layers.


The use of water-saving methods to reduce the amount of water needed for homes, lawns, farming and industry and thus increase water supplies for optimum long-term economic and social benefits.


Any substance that when added to water (or another substance) makes it impure and/or unfit for consumption or use.


Any substance that “eats away” (corrodes) another substance usually by chemical reaction.


A structure built to prevent or slow the flow of water in a stream, river or lake.


The location where a river meets the ocean or other marine environment. It is often characterized by a “fanning” of the river channel into a series of shallow wetlands and channels of fresh, salt and/or brackish water.


The loss of water from surface water reservoirs or ground water aquifers at a rate greater than that of recharge.


The removal of salts and other minerals from water to make it potable (drinkable).


A geographical area characterized by receiving less than 10 inches of liquid precipitation per year. Deserts can be hot, as in the American Southwest, or cold as in Antarctica.


Atmospheric water that has condensed onto cooler objects. This usually occurs at night, when the relative humidity rises and the air temperatures cool.


Reducing the concentration of a chemical or compound by adding a second or third chemical/compound to a mixture.


An outflow of water from a stream, pipe, ground water system or watershed.


To cause one or more compounds to break apart and become absorbed in a liquid solution, such as mixing salt or sugar into water.

Dissolved Oxygen

Microscopic bubbles of oxygen that can be found within water.


In the direction of a stream’s current; in relation to water rights, refers to water uses or locations that are affected by upstream uses or locations.


(1) An area of land in which a body of water drains. (2) The ability of soil to allow water to percolate to the layers beneath.


An extended period with below-average precipitation; often affects crop production and availability of water supplies.


A community of living organisms and their interrelated physical and chemical environment; also, a land area within a climate.


All of the external factors, conditions, and influences that affect an organism or a biological community.


The location where a river or stream meets the ocean. These areas are unique and often contain high levels of biodiversity.


Water from water bodies (lakes, streams, creeks etc.) changes from a liquid (gaseous state) and rise into the air. Sunshine, wind and warmer air can speed up the rate of evaporation.


The loss of water from the soil through both evaporation and transpiration from plants.


The process by which a chemical coagulant added to the water acts to facilitate bonding between particles, creating larger aggregates which are easier to separate. The method is widely used in water treatment plants and can also be applied to sample processing for monitoring applications.


An overflow of water that submerges or “drowns” land.


A cloud of condensed water that forms at ground level.

Fresh Water

Water with less than 0.5 parts per thousand dissolved salts.

Gallons Per Minute (GPM)

A measurement usually associated with human water use, in homes, agriculture or industry.


The state of water in which individual molecules are highly energized and move about freely; also known as vapor.


A large body of collected snow and ice formed over many years that slowly moves through a valley or down a mountain.


The water beneath the surface of the ground, consisting largely of surface water that has seeped down; the source of water in springs and wells.


Frozen precipitation produced by thunderstorms where round stones of ice are formed in various sizes.

Hard Water

Water that has high mineral content.


The source of a stream or river

Hot spring

An area where underground water, which has been heated geothermally, seeps to the surface.

Hundred Cubic Feet (HCF)

A measure of volume intended to symbolically represent 100 squares each measuring 1 foot wide, 1 foot long and 1 foot high.


A gaseous element that is one of the components of a water molecule.


The controlled application of water to croplands, hay fields and/or pasture to supplement the water supplied by nature.

Imported Water 

Imported water consists primarily of water obtained from the State Water Project, LA Aqueduct, and Colorado River. Water retailers purchase imported water from local contractors or regional wholesale water agencies. Most water agencies get some source of Imported Water and mix it with local ground water.


A room or building equipped for scientific experiments, research, or teaching, or for the manufacture of chemicals.


A natural or man-made body of fresh or salt water surrounded by land.


The state of water in which molecules move freely among themselves but do not separate like those in a gaseous state.


A term applied to faucets, toilets and showerheads that are engineered to reduce the flow of water but still function suitable.


Million Gallons per Day.

Nonpoint source pollution

Widespread overland runoff containing pollutants; the contamination does not originate from one specific location, and pollution discharges over a wide land area.


The diffusion of water through a membrane.


A gaseous element that is one of the two components of a water molecule. It is also the most abundant element on Earth and essential for plants and animals to breathe.

Parts Per Million (PPM)

Units typically used in measuring the number of “parts” by weight of a substance in water; commonly used in representing pollutant concentrations.


The movement of groundwater down through open pores in the soil and underlying rock by the forces of gravity.


The fluid secreted in the form of sweat by the sweat glands and as water that diffuses through the skin by humans and some other animals that helps lower an elevated body temperature.


A classification of acid or base materials on a scale of 0 to 14, with 7 representing neutrality; numbers less than 7 indicate increasing acidity, and numbers greater than 7 indicate increasing alkalinity (basic conditions).


The process through which green plants (and certain other organisms) produce simple sugars by combining carbon dioxide and water using light (sunlight) as an energy source and producing oxygen as a by-product.

Point source pollution

Pollutants discharged from any identifiable point, including pipes, ditches, channels, sewers, tunnels and containers of various types.


Any chemical or object which is unnatural in an ecosystem such that it will cause harm to the soil, water, air or life that is found there. Pollutants can include oil, pesticides and runoff containing road salt and trash.


An alteration in the character or quality of the environment, or any of its components, that renders it less suited for certain uses.

Potable Water

Water safe enough to be consumed by humans.


Water falling, in a liquid or solid state, from the atmosphere to Earth (e.g., rain, snow).


Water in liquid form dropped from clouds as precipitation.


The replenishment of water into a system by precipitation or flow from another location.

Recycled Water

Former wastewater (sewage) that is treated to remove solids and certain impurities, and used in sustainable landscaping irrigation.


A man-made structure, usually an artificial lake, designed to store water.


A natural stream of fresh water flowing through a channel towards the sea.


Precipitation that flows overland to surface streams, rivers and lakes.

Salt water

Water that contains a relatively high percentage (over 0.5 parts per thousand) of salt minerals.


The process of settling or being deposited as a sediment.


Waste that is suspended and moved in water. It contains bacteria, protozoa and viruses that normally live in the intestines of humans and other animals.


Refers to the residual, semi-solid material left from industrial wastewater or sewage treatment processes.


Water in a solid, hexagonal, crystalline form dropped from clouds as precipitation.

Source Water

The site where water is collected for use. It can be a lake, reservoir, river, aquifer or some other body of water.

State Water Project

The California State Water Project (SWP) is a water storage and delivery system of reservoirs, aqueducts, power plants and pumping plants. Its main purpose is to store water and distribute it to 29 urban and agricultural water suppliers in Northern California, the San Francisco Bay Area, the San Joaquin Valley, the Central Coast, and Southern California. Of the contracted water supply, 70 percent goes to urban users and 30 percent goes to agricultural users.

Storage Tanks

Man-made structures intended to store water or other liquid or gaseous items that can be used at a later time.

Storm Water

The water resulting from a weather event that has run off impervious man-made surfaces such as streets and parking lots into nearby sewers or waterways.


Any body of running water moving under gravity’s influence through clearly defined natural channels to progressively lower levels.

Surface Water

Water above the surface of the land, including lakes, rivers, streams, ponds, floodwater and runoff.


The slang term applied to a faucet or other potable water outlet.


The process by which water absorbed by plants (usually through the roots) is evaporated into the atmosphere from the plant surface (principally from the leaves).


A long narrow area in the soil or at the bottom of the ocean that is deeper than the surrounding land.


A stream that contributes its water to another larger stream or body of water.


The cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air.

Water Cycle

The paths water takes through its various states—solid, liquid and gas—as it moves throughout Earth’s systems (oceans, atmosphere, groundwater, streams, etc.).

Water Footprint

A term used to denote the water usage of an individual, company or community.

Water Meter

A man-made device installed along water pipes to calculate the amount of water that moves through cities or it is used by businesses and homeowners.

Water Pressure

The downward force of water upon itself and other materials; caused by the pull of gravity.

Water Quality

The chemical, physical, and biological characteristics of water with respect to its suitability for a particular use.

Water Right

A legal right to use a specified amount of water for beneficial purposes.

Water Source

A body of water that acts as a source for human use. This can be surface water (lake, reservoir, and river) or groundwater (aquifer).


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

Water Table

The top of an unconfined aquifer; indicates the level below which soil and rock are saturated with water.

Water Treatment Plant

Facilities that treat water to remove contaminants so that it can be safely used.


A narrow hole or pipe dug into the earth to access groundwater.


A land area that is saturated with water, either permanently or seasonally, such that it takes on the characteristics of a distinct ecosystem.


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