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California State Water Project 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.

California Water Balance Summary
For Water Years 1998, 2000 and 2001
Where the Water Goes
1998 (Wet Year)
2000 (Avg Year)
2001 (Dry Year)
Total Supply
(Precipitation & Imports)
335.8 million acre-feet 194.2 million acre-feet 145.5 million acre-feet
Dedicated Supply (Includes Reuse) 97.5 million acre-feet 82.5 million acre-feet 65.1 million acre-feet

Distribution of Dedicated Supply to Various Applied Water Uses
Where the Water Goes
1998 (Wet Year)
2000 (Avg Year)
2001 (Dry Year)
Urban Uses 7.7 million acre-feet (8%) 8.8 million acre-feet (11%) 8.6 million acre-feet (13%)
Agricultural Uses 27.7 million acre-feet (28%) 34.3 million acre-feet (42%) 34.1 million acre-feet (52%)
Environmental Water 62.1 million acre-feet (64%) 39.4 million acre-feet (47%) 22.4 million acre-feet (35%)