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What Are Some California Water Sources?

Water sources are a matter of concern for many California communities, as well as a cause of conflict. Abundant water supplies and urban population centers seldom coincide in this state with five separate climate zones, ranging from coastal areas with plentiful rainfall to extremely arid deserts. While many towns and cities rely on local sources, others depend on elaborate aqueduct systems to transport their water supplies hundreds of miles from the source.

  1. Local Water Sources

    • Groundwater is created when rain or melting snow seeps into the ground, filling up tiny spaces in the sand, gravel or silt that makes up the soil. This underground aquifer is tapped by digging wells and installing pumps to bring the water to the surface. In a year with normal amounts of rain, about 30 percent of California's water supply comes from groundwater; but, during a drought, groundwater may account for up to 60 percent of the state's drinking water. However, the percentage of groundwater in each city's supply varies according to local conditions. Reservoirs and dams on local waterways, built and operated by local public water districts, private companies and county or city water departments are other local water sources.

    Statewide Water Projects

    • As long ago as 1919, geologist Robert Marshall proposed a statewide water project. His ideas led to the construction of the Central Valley Project by the federal government during the 1930s. The system includes 500 miles of aqueducts and canals, as well as 20 reservoirs with a total capacity of 11 million acre-feet. (One acre-foot is the volume of water required to cover one acre of land at a depth of one foot. It is equivalent to 325,851 gallons.) In addition, the State Water Project, operated by the California Department of Water Resources, carries water through a 444-mile-long aqueduct from Oroville Dam on the Feather River to Lake Perris near Riverside.

    Other Aqueduct Systems

    • In northern California, two systems transport water from the Tuolomne and Mokelumne rivers to San Francisco and cities in the East Bay region, while the Colorado River supplies 4.4 million acre-feet annually to southern California cities and agriculture. However, the most controversial, project in the state draws water from Mono Lake and the Owens River on the east slope of the Sierra Nevada to supply the city of Los Angeles. Early in the 20th century, the city's Department of Water, under Superintendent William Mulholland, acquired the necessary land to build a 223-mile aqueduct to Los Angeles. The system carried away nearly all of the Owens Valley's water, leaving it dry and barren. Controversies regarding water rights and allegations of questionable financial dealings continue to erupt over this project.

    Future Water Supplies

    • Climate change is expected to decrease the Sierra Nevada snowpack, currently the source of approximately 65 percent of the state's water, by 25 percent as soon as 2050. Rainfall is more difficult to capture and store than snowmelt, so increased precipitation in the form of rain may lead to decreasing water supplies. At the same time, increasing variability in weather patterns may mean more frequent droughts.

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