Water Supply

In average water years like 2000, California receives about 200 million acre-feet of water from precipitation and imports from Colorado, Oregon and Mexico. Of this total supply, about 50-60 percent either is used by native vegetation, evaporates to the atmosphere, provides some of the water for agricultural crops and managed wetlands (effective precipitation); or flows to Oregon, Nevada, the Pacific Ocean, and salt sinks like saline groundwater aquifers and the Salton Sea. The remaining 40-50 percent, or dedicated supply, is distributed among urban and agricultural uses, water for protecting and restoring the environment, or storage in surface and groundwater reservoirs for later use.

In any year, some of the dedicated supply includes water that is used multiple times (reuse) and water stored from previous years. Ultimately, about a third of the dedicated supply flows out to the Pacific Ocean, in part to meet environmental requirements, or to other salt sinks.For wet and dry years, the total supply and the distribution of the dedicated supply to various uses differ significantly from the example above for an average year. This is illustrated in the table below for water years 1998 (wet), 2000 (average) and 2001 (dry).

For more information on the state's recent water supplies and uses, see the California Water Plan Update (currently available in draft form at www.waterplan.water.ca.gov).

California Water Balance Summary
For Water Years 1998, 2000 and 2001

* Environmental water includes instream flows, wild & scenic flows, required Delta Outflow and managed wetlands water use.

** million acre-feet