Acre-foot

This unit of measurement is used in the water industry to describe large quantities of water, such as the capacity of a reservoir. One acre-foot equals approximately 326,000 gallons, or enough water to cover one acre of land (about the size of a football field) one foot deep in water. One acre-foot of water is enough to meet the needs of an average family for two years.

Activated Sludge

The biological process that removes organic matter from wastewater using microscopic plants and animals (organisms). The activated sludge process imitates the natural process that a river, lake or stream uses to clean itself.

Advanced Treatment

Additional treatment processes used to clean wastewater even further following primary and secondary treatment. Also known as tertiary treatment.

Aeration Tank

A chamber in which air is injected into wastewater to allow microscopic organisms to clean the water (see Activated Sludge).

Algae

The simplest kind of green plants, usually found growing in damp or wet places.

Aqueduct

A constructed system of canals, channels and/or pipelines to move water from one location to another. Irvine Ranch Water District receives about 50 percent of its water through the Colorado River Aqueduct and the California Aqueduct.

Aquifer

Underground rock, sand or gravel formations which store water. Irvine Ranch Water District supplies about 50 percent of its water needs from the aquifers that make up the Orange County Groundwater Basin.

Arid

Dry; deserts are arid places. Semi-arid refers to a place that is almost as dry as a desert.