Over the past three full water years, California could have exported 33.1 million acre-feet of water from the Sacramento-San Joaquin Delta—more than twice the 14.2 million acre-feet actually exported—if the state had captured all flow to San Francisco Bay exceeding 15 million acre-feet annually, according to an analysis published June 17, 2026, by Edward Ring, Director of Water and Energy Policy at the California Policy Center. The report argues that California should establish a maximum delta outflow threshold necessary to preserve ecosystem health, and treat any flow beyond that amount as available for diversion to farms and cities.
The report presents delta inflow and export data for the last seven water years showing massive variation between wet and dry periods. In 2023, 27.2 million acre-feet flowed to the bay with 5.2 million acre-feet exported, while 2024 saw 18.1 million acre-feet to the bay and 4.2 million acre-feet exported. By contrast, the dry year of 2021 delivered just 4.1 million acre-feet to the bay with only 1.5 million acre-feet exported. The 2025 water year recorded 18.6 million acre-feet flowing to the bay and 4.8 million acre-feet exported, while the current 2026 water year through June 15 has seen 12.9 million acre-feet reach the bay with 2.7 million acre-feet exported. If the state and federal pumps operated at 100 percent capacity for 100 days and 40 percent capacity for the remaining 265 days each year, they could move 6.2 million acre-feet annually.
According to Ring, California needs "a combination of more storage upstream from the delta, greater capacity to safely withdraw water from the delta, and more storage downstream along the aqueducts" to capture tens of millions of additional acre-feet. The report states that water can be more safely extracted through "a combination of dredging, strategically placed gates and barriers throughout the delta, and fish friendly diversion basins." Ring writes that Bay Area cities "would have to finally find the wherewithal to clean up their sewage, since no amount of delta outflow flushing out the SF Bay is enough to fully remove a perennial outfall of roughly 400,000 acre feet per year of nitrogen rich effluent." The report suggests that if the bay was cleaned up, salinity managed, and habitat restored, "the magic outflow number might drop to 12 million acre feet per year," which would have made an additional nine million acre-feet available over the past three years.
The analysis explains that underground storage offers what Ring calls "limitless capacity" for capturing wet-year surpluses. At a moderate to high permeability rate of 0.5 feet per day, inundating 20,000 acres for 100 days could store one million acre-feet. For soils with lower permeability—three inches per day, described as a common soil type—storing two million acre-feet in a single winter would require flooding 80,000 acres, which represents less than 2 percent of total irrigated farmland in the San Joaquin Valley. The report notes these percolation basins "can also serve as flood bypasses and valuable seasonal habitat." Ring argues that if farmers received full contracted water allocations during wet years to make up for dry-year deficits, they'd be incentivized to rapidly recharge aquifers, with the caveat that "more water must go into the ground than comes out" until water tables are restored.
The report concludes that water agencies and irrigation districts deserve certainty rather than a moving target, calling on Sacramento to establish a firm outflow threshold. Ring frames the challenge as developing the capacity to "take the so-called big gulp during wet winters" through restored aqueduct capacity, safer delta extraction methods, and massive underground storage expansion. The bottom line: California is letting tens of millions of acre-feet flow to the ocean each wet year that could instead recharge depleted aquifers and supply farms and cities—if the state picks a number and builds the infrastructure to capture everything above it.