While the Colorado River remains San Diego's largest water source and has been in decline for years, the county would not face immediate drought if deliveries ceased. The region has cultivated a multi-faceted approach to water supply, leveraging existing infrastructure and developing new technologies to build resilience.
Central to San Diego's current strategy is the Claude "Bud" Lewis Carlsbad Desalination Plant, which began commercial operations in 2015. Located beside Agua Hedionda Lagoon, this facility utilizes reverse-osmosis membranes to convert Pacific seawater into approximately 50 million gallons of drinking water daily. A 10-mile pipeline transports this treated water inland to the Water Authority's aqueduct system at San Marcos. The plant operates independently of snowfall in the Colorado River's headwaters and contributes about 10% of the region's water supply. However, its production capacity and electricity supply limit its output, and its current gallons already meet existing demand rather than serving as an additional replacement for lost imports.
Conservation agreements also play a significant role. Through concrete lining along the All-American and Coachella canals, the San Diego County Water Authority has secured 77,700 acre-feet annually. A separate agreement with the Imperial Irrigation District provides an additional 200,000 acre-feet each year. These supplies are tied to senior-priority Colorado River rights, which offer protection during shortages. The Metropolitan Water District of Southern California (MWD) also imports Colorado River water via its 242-mile aqueduct, extending between Lake Havasu and Lake Mathews near Riverside. A complete loss of river deliveries, however, would put both these conservation transfers and MWD's Colorado imports at risk.
Emergency storage is a critical component of the region's water security. The San Vicente Dam was raised 117 feet, creating an additional 52,100 acre-feet of emergency storage capacity and approximately 100,000 acre-feet of carryover capacity for dry periods. This facility is integrated into a regional emergency system that connects reservoirs with pipelines and pumping stations, enabling stored supplies to reach water agencies if imports are interrupted. Its reserves would help cover a sudden loss, providing time for officials to adjust deliveries and consumption. The City of San Diego also operates nine supply reservoirs that capture local runoff and store imported water, with local rainfall capable of replenishing some of these stores.
Beyond Colorado River imports, the State Water Project delivers water from Northern California's Sacramento-San Joaquin Delta, including water stored at Lake Oroville, southward via the California Aqueduct. MWD supplies the San Diego region through its distribution network. However, extra deliveries from this source are contingent on conditions farther north and MWD's available capacity, as other Southern California communities also depend on this supply, potentially leading to widespread shortages during a drought.
San Diego is also making substantial investments in wastewater recycling for potable use. The North City Pure Water Facility in the University City area is under construction, designed to provide 30 million gallons a day of purified water through advanced treatment, including reverse osmosis and ultraviolet light with advanced oxidation. Purified water will enter Miramar Reservoir before passing through the drinking-water treatment system. Discharge into the reservoir is expected to commence in 2026, with full Phase 1 rates coming online as remaining facilities are commissioned through 2026. Therefore, the full 30 million gallons cannot currently be considered an already operating emergency supply. The larger program aims for 83 million gallons daily by 2035, projected to cover nearly half the City of San Diego's supply needs. A separate East County project is designed to send purified water to Lake Jennings, producing up to 11.5 million gallons daily.
In Chula Vista, the Richard A. Reynolds Groundwater Desalination Facility draws brackish groundwater from the Sweetwater River area, processing up to 10 million gallons daily using reverse osmosis. The City of San Diego co-funded its expansion and holds an allocation of up to 2,600 acre-feet annually.
Additionally, the city's separate recycled-water system supplies approved irrigation and industrial uses through specially marked purple equipment, with treatment provided by the North City and South Bay reclamation plants. This reduces the volume of water drawn from drinking-water supplies for non-potable uses. A prolonged loss of Colorado River deliveries would likely necessitate tighter limits on water use, and reducing demand would slow withdrawals from emergency storage, providing crucial time for other regional sources to bear a greater share of the load.
