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| Water supply in California | |
|---|---|
| Name | California water |
Water supply in California California's water supply is a complex system shaped by geography, climate, law, and infrastructure. The state relies on a mosaic of storage, conveyance, groundwater, and diversions spanning the Sierra Nevada, Sacramento River, San Joaquin River, and coastal waters, managed through institutions such as the California Department of Water Resources, State Water Resources Control Board, and local Metropolitan Water District of Southern California. Historic projects including the California State Water Project and the Central Valley Project underpin delivery to urban centers like Los Angeles and San Francisco, and agricultural hubs in the Central Valley.
California's hydrology is governed by the Mediterranean climate of the Pacific Ocean coastline, the orographic precipitation of the Sierra Nevada, and the rainshadow of the Mojave Desert. Major legal frameworks include the California Constitution water rights provisions, the Water Rights Act-era doctrines, and federal statutes such as the Endangered Species Act and the Clean Water Act, which interact with agencies like the U.S. Bureau of Reclamation and the U.S. Environmental Protection Agency. Significant events shaping supply include the California Water Wars, the 1976–77 drought, the 2012–2016 drought, and reactions informed by research from institutions like the University of California, Davis and the Stanford University Water in the West program.
Surface water originates primarily from the Sacramento–San Joaquin River Delta, the Feather River, the Trinity River, and the American River, captured in reservoirs such as Shasta Lake, Oroville Dam, Don Pedro Reservoir, and Lake Tahoe. Groundwater basins beneath the San Joaquin Valley, Tulare Basin, and the South Coast supply wells for cities like San Diego and Bakersfield. Recycled water programs in Orange County, desalination at facilities such as the Carlsbad Desalination Plant, and transfers from the Colorado River via the Colorado River Aqueduct supplement supplies for the Metropolitan Water District of Southern California and Imperial County agriculture. Snowpack in the Sierra Nevada functions as a natural reservoir, monitored by the California Department of Water Resources snow surveys and influenced by El Niño–Southern Oscillation and Pacific Decadal Oscillation variability.
Major conveyance systems include the California Aqueduct, the Delta-Mendota Canal, and the Central Valley Project canals, linked to dams like Folsom Dam and Trinity Dam. Urban distribution networks are operated by entities such as the Los Angeles Department of Water and Power, the San Francisco Public Utilities Commission, and local water districts like the East Bay Municipal Utility District and the Sacramento Municipal Utility District (for joint projects). Interties, pumping plants, and levee systems in the Sacramento–San Joaquin Delta connect to storage in reservoirs managed by the U.S. Bureau of Reclamation and the California Department of Water Resources, while canals, aquifers, and conveyance links cross federal lands of the U.S. Forest Service and state holdings administered by the California Natural Resources Agency.
State-level planning is coordinated through the California Water Action Plan, integrated regional plans under the Sustainable Groundwater Management Act, and regulatory oversight by the State Water Resources Control Board. Federal involvement arises via the U.S. Bureau of Reclamation operations, the U.S. Fish and Wildlife Service consultations, and court adjudications such as cases heard in the U.S. District Court for the Eastern District of California. Water markets and transfers are shaped by precedents like the Mono Lake controversies and policy instruments developed at California Legislative Analyst's Office briefings. Local governance includes county boards of supervisors in Los Angeles County, Alameda County, and Santa Clara County, along with special districts such as the Irrigation Districts and the Santa Clara Valley Water District.
Diversions and dam operations affect habitats for species listed under the Endangered Species Act including the Delta smelt, Chinook salmon, and Steelhead trout. Delta levee subsidence and sea-level rise threaten the Sacramento–San Joaquin River Delta ecosystem, while agricultural runoff from the Central Valley Project service areas contributes to issues addressed under the Clean Water Act. Restoration projects engage organizations such as The Nature Conservancy, California Department of Fish and Wildlife, and the National Oceanic and Atmospheric Administration to rehabilitate wetlands, riparian corridors, and estuarine habitat in places like the Sacramento National Wildlife Refuge and San Pablo Bay National Wildlife Refuge.
Drinking water standards are enforced under frameworks administered by the California Department of Public Health and the U.S. Environmental Protection Agency, with contaminants monitored including nitrates in Kern County wells, arsenic in El Dorado County sources, and emerging contaminants like per- and polyfluoroalkyl substances addressed in advisories from the California Office of Environmental Health Hazard Assessment. Public utilities such as the Metropolitan Water District of Southern California and the San Diego County Water Authority operate treatment plants adhering to standards set by the Safe Drinking Water Act and state regulations; crises such as lead contamination in the City of Flint context have informed policymaking and public communication statewide.
Key challenges include prolonged droughts influenced by climate change, legal battles involving the Sierra Club and water users, subsidence in the San Joaquin Valley, and competing demands from agriculture in Fresno County and urban growth in Orange County. Adaptive strategies incorporate managed aquifer recharge projects piloted by the California Department of Water Resources, investments in desalination and recycling led by agencies like the Metropolitan Water District of Southern California, and regional collaboration under initiatives promoted by the Public Policy Institute of California and research centers at University of California, Berkeley and California State University, Sacramento. Planning also engages bond measures approved by the California State Legislature and ballot propositions to fund infrastructure and ecosystem restoration.