California has built a water delivery infrastructure capable of moving a drop of water that originates near the northern border all the way down south to the Mexican border. Most of California’s water comes from rain and snow that falls in northern and eastern parts of the state. Two-thirds of the Los Angeles region’s water supply is imported from sources hundreds of miles away.
One-third of our water supply comes from local resources such as groundwater from local aquifers, surface water stored in reservoirs, recycled water from water reclamation plants, and local reuse of greywater.
Groundwater is a crucial component of the state’s water supply, representing over 1/3 of water used in an average year. However, its use varies by location: some communities have no groundwater and rely solely on surface water while other communities may only have groundwater; still other communities rely on a combination of imported water and groundwater, and some even rely entirely on imported water.
This is the largest estuary on the coast, where the Sacramento and San Joaquin rivers meet. It is the hub of California’s water system. Water from the Central Valley Project and the State Water Project flow through here.
The largest state-built delivery system in America, it is run by the Department of Water Resources. The project begins at Oroville Dam on the Feather River, picks up water from additional lakes and rivers and brings it through reservoirs, canals and pipelines to the Sacramento-San Juaquin Delta, where the water is pumped to the 444-mile-long California Aqueduct and channeled to 26 million people and 750,000 acres of farmland throughout the state.
The 1,450-mile-long Colorado River passes through parts of seven states and several Indian reservations. 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.
Owned and operated by the Metropolitan Water District, it picks up Colorado River water at Lake Havasu, Arizona, and takes it 242 miles to Lake Mathews in Riverside County, from where it is distributed among MWD’s 26-member agencies.
Aqueducts built by the City of Los Angeles draw water from the Owens River, Mono Lake Basin and reservoirs on the east slopes of the southern Sierra. In Los Angeles, a 223-mile aqueduct completed in 1913 has served as a major water supply source, conveying water from the Owens River in the eastern Sierra. It takes roughly 8 days for a drop of water to travel along the Los Angeles Aqueduct from the Mono Basin to Los Angeles County. A second aqueduct, completed in 1970, added another 50 percent capacity to the water system. Designed under the supervision of William Mulholland, it carries water more than 200 miles from Eastern Sierra into Southern California, driven entirely by gravity. Mono Lake Water level must be maintained at 6,392 feet above sea level to protect bird breeding and stream habitat.
Dams play a crucial role in effective stormwater management by restricting water flows and forming reservoirs that store water for later use. The result is minimized flood risk and stored water that can be used to recharge groundwater.
When water is released from reservoirs, storms, recycled and imported sources, it may be diverted to spreading grounds, which are specifically designed to infiltrate water into underground aquifers to replenish groundwater. An aquifer is an underground reservoir made up of porous soil through which water can easily move. The water contained within these soils is called groundwater.
The expanding population of the region relies on large volumes of groundwater to meet its water supply needs. As water is extracted from underground aquifers, a lowering water table can allow seawater to flow inland and contaminate groundwater. To prevent seawater intrusion, a series of injection wells along the coast pump fresh water into the aquifer to raise the elevation of groundwater. The injected fresh water serves as a barrier, keeping seawater out and protecting our groundwater resources.
Recycled water from water reclamation plants is also used for nonpotable uses, such as watering parks and golf courses, throughout the region.