The glossary for the California Water Plan provides 31 pages of definitions of terms that can help us to understand water issues. Click to view the full Water Plan Glossary.

For example:

Acre-foot (af) – The volume of water that would cover one acre to a depth of one foot; equal to 43,560 cubic feet or 325,851 gallons.

Groundwater –Water that occurs beneath the land surface and fills the pore spaces of the alluvium, soil, or rock formation in which it is situated. It excludes soil moisture, which refers to water held by capillary action in the upper unsaturated zones of soil or rock. Groundwater classified as underflow of a surface water system, a “subterranean stream flowing through a known and definite channel,” is subject to statutory permitting process. However, most groundwater in California is presumed to be “percolating water,” that is, water in underground basins and groundwater which has escaped from streams and is not subject to a permitting process. See also subterranean stream.

Watershed – The land area from which water drains into a stream, river, or reservoir.

Glossary written by California Department of Water Resources.