In 1960, California voters approved financing for construction of
the initial features of the State Water Project (SWP). The
project includes some 22 dams and reservoirs, a Delta pumping
plant, a 444-mile-long aqueduct that carries water from the Delta
through the San Joaquin Valley to southern California. The
project begins at Oroville Dam on the Feather River and ends at
Lake Perris near Riverside. At the Tehachapi Mountains, giant
pumps lift the water from the California Aqueduct some 2,000 feet
over the mountains and into southern California.
The 1,440-mile-long Colorado River passes through parts of seven
states, several Indian reservations and the Republic of Mexico.
California is entitled to 4.4 million acre-feet of water annually
from river. Most of that water irrigates crops in the Palo Verde,
Imperial and Coachella valleys, located in the southeastern
corner of the state, but the Colorado also is a vital source of
water for urban southern California. Urban supplies are
distributed by the Metropolitan Water District of Southern
California through its Colorado River Aqueduct.
About 30 percent of California’s total annual water supply comes
from groundwater in normal years, and up to 60 percent in drought
years. Local communities’ usage may be different; many areas rely
exclusively on groundwater while others use only surface water
supplies. Contrary to popular opinion, groundwater does not exist
in underground lakes. Groundwater fills pores (spaces) between
sand, gravel, silt and clay in water-bearing formations known as
Many cities rely on local water projects for all or a portion of
their supplies. These projects typically were built and are
operated by local public water districts, county water
departments, city water departments or other special districts.
Nearly 600 special purpose local agencies in California provide
water to their areas through local development projects and
imported supplies. A number of local agencies may also operate
flood control and wastewater treatment facilities in addition to
providing drinking water.