By Jose E. Navarro | The Navarro Report | California Affairs
California’s water story this year is really two stories, and they are almost mirror images of each other. In San Diego County, decades of infrastructure investment have produced something almost unheard of in the arid Southwest: a water agency with more supply than its customers need, actively shopping that surplus to other regions. In the San Joaquin Valley, a newly released federal water plan projects an annual supply-demand gap of 2.5 million acre-feet by 2040 — a deficit that could pull a million acres out of farm production and cost the region $7.2 billion a year. The two stories share a state, a drought-stressed river basin, and increasingly, a set of policymakers eager to describe one as a partial answer to the other. It isn’t, and the distance between the two systems is worth walking through carefully.
How San Diego built a surplus
The San Diego County Water Authority’s surplus is not an accident of rainfall; it is the product of roughly three decades of deliberate over-investment in supply reliability. The region diversified away from near-total dependence on imported water through the Claude “Bud” Lewis Carlsbad Desalination Plant, which has turned Pacific Ocean water into drinking water since 2015 and now supplies about 10 percent of the county’s water. It added the Pure Water San Diego recycling program, expanded reservoir and aqueduct capacity, and locked in a long-term Colorado River transfer agreement with the Imperial Irrigation District under the Quantification Settlement Agreement. At the same time, conservation drove down demand faster than planners forecast. The result, according to the Water Authority’s own 2026 Urban Water Management Plan, is a region projected to have ample supply through 2050 even across multiple dry years — while carrying some of the most expensive water in the state, because ratepayers financed all of that redundancy.
Rather than let that investment sit idle, the Water Authority has spent 2026 monetizing it. In March, it signed a 21-year deal to sell at least 10,000 acre-feet a year to the Western Municipal Water District in Riverside County for $13.5 million annually, plus $40 million upfront for a three-year drought reserve. A second agreement with Eastern Municipal Water District is expected to generate roughly $74 million in new revenue, and in August the authority added a third transfer agreement with the city of Burbank. Board Chair Nick Serrano called the Western deal a way to “maximize the value of the investments San Diego County residents made over decades” while being “mindful of affordability” — language that reflects the real purpose here: offsetting the rate increases that expensive desalinated and recycled water would otherwise require.
The bigger, untested move: trading water across state lines
The more consequential development came in June, when the Water Authority, the Metropolitan Water District of Southern California, the U.S. Bureau of Reclamation, and agencies in Arizona and Nevada signed a memorandum of understanding at the Carlsbad plant to explore something that has never been done within the Colorado River Basin: an interstate water exchange. The concept is straightforward on paper. San Diego would draw more of its supply from desalination and recycled water, and in exchange would leave a corresponding volume of its Colorado River allocation in the river system, where agencies like Arizona’s Central Arizona Project or the Southern Nevada Water Authority could draw on it instead, for a price. Dan Denham, the Water Authority’s general manager, called it a potential “gamechanger for the entire Southwest.”
The numbers attached to the pilot are modest by design. Officials have discussed making roughly 10,000 acre-feet available for interstate transfer within six months to a year, with a longer-term ceiling — counting recycled water and reuse projects — of perhaps 100,000 acre-feet, enough to supply Phoenix for about three months. The deal still requires sign-off from Metropolitan, the Bureau of Reclamation, and the Central Arizona Project before a single acre-foot moves. It arrives against a genuinely stressed backdrop: Lake Mead sits at roughly 35 to 36 percent of capacity, and on Aug. 21 the Interior Department ordered California, Arizona and Nevada to further cut their Colorado River draws.
Why it barely touches the San Joaquin Valley’s problem
Here is where the connection to the San Joaquin Valley’s shortfall breaks down. San Diego’s water — desalinated, recycled, or transferred from the Imperial Valley under the Quantification Settlement Agreement — is not physically or contractually part of the State Water Project and Central Valley Project system that irrigates San Joaquin Valley farmland. There is no pipeline, canal or legal mechanism by which San Diego’s surplus reaches Fresno, Kern or Tulare counties. The Valley’s projected 2.5-million-acre-foot annual gap, laid out this month in the congressionally authorized Unified Water Plan prepared by the California Water Institute at Fresno State, the Water Blueprint for the San Joaquin Valley and Stantec, is driven by an entirely different set of forces: the Sustainable Groundwater Management Act’s pumping restrictions across sixteen subbasins, shrinking environmental flows, and climate-driven changes in snowpack timing. None of that is affected by how much water San Diego sells to Riverside County.
The one place the two systems genuinely touch is Metropolitan Water District, which imports both Colorado River water and State Water Project water to serve 19 million people across six Southern California counties. When Colorado River allocations shrink, Metropolitan leans more heavily on its State Water Project supply — the same Delta exports that also move water south to San Joaquin Valley agriculture and to Valley cities’ own State Water Project contracts. If the San Diego-Arizona-Nevada exchange eventually frees up meaningful Colorado River water for the basin, it could, in theory, ease some of that competitive pressure on Delta exports. But at a ceiling of 100,000 acre-feet against a 2.5-million-acre-foot annual Valley deficit, the math is unforgiving: even in the most optimistic long-term scenario, and even if every drop of freed-up Colorado River water reduced Metropolitan’s Delta draw one-for-one, the interstate exchange would offset roughly 4 percent of the Valley’s projected 2040 gap. The pilot phase moving 10,000 acre-feet would offset a small fraction of 1 percent.
The Unified Water Plan itself does not list San Diego’s surplus, or the interstate exchange, among its near-term priorities. Its ask is for dedicated state and federal investment in storage, conveyance and groundwater recharge across the Valley’s sixteen subbasins — a recognition that the region’s deficit has to be closed with Valley-specific infrastructure and funding, not with water that legally cannot reach it. San Diego’s surplus is a genuine California water success story, the product of ratepayers financing diversification years before the current drought made it fashionable. It is also, structurally, a story that belongs to the Colorado River Basin and Southern California’s coastal supply portfolio — not a lever that closes the San Joaquin Valley’s gap. Policymakers citing one to reassure the public about the other should be precise about which system they are describing.
Human-Directed AI Journalism: This article was researched and drafted with AI assistance under the direction, editing, and final approval of Jose E. Navarro.