California Can Dramatically Increase Its Water Supply
Two imminent federal actions promise to greatly influence water policy in California for the next several years. The first arises out of an executive order from President Donald Trump to the secretary of the interior to restart the work “to route more water from the Sacramento-San Joaquin Delta to other parts of the state for use by the people there who desperately need a reliable water supply.” The deadline for the secretary to report back to the president is April 20, a few days from now.
The second is, if anything, more significant. There are two finalists under consideration by the White House Presidential Personnel Office to become the commissioner of the Bureau of Reclamation. One of them is a Californian, the other is from Arizona. Advocates for the Arizonan choice represent some, but not all, of the other six states that draw water from the Colorado River. They’re concerned that a Californian would not sufficiently take into account their states’ interests.
This is a mistake for two reasons. The first is that California’s candidate has already demonstrated to many people who represent water interests outside of California a fair-minded and collaborative approach to Colorado River allocations and has earned their support. There are solutions whereby every state along the Colorado watershed can have as much water as it needs, and California’s candidate to take over the bureau may be uniquely motivated and qualified to implement them. The American Southwest needs a commissioner who knows what California needs for one compelling reason: Only California has the ability to increase its water supply. None of the other states involved — Wyoming, Utah, Colorado, New Mexico, Nevada, or Arizona (or Mexico, for that matter) — can do anything to help their water situation apart from rationing consumption and praying for rain. The reason to appoint a (fair-minded) Californian to the job is not to deprive the other Southwestern states of the Colorado’s water but to increase the supply of California’s own water from other sources, reducing California’s dependence on Colorado River water.
California can dramatically increase its usable water supply through investment in new water supply infrastructure. Currently, California’s farmers rely on 30 million acre-feet per year for irrigation, and the state’s cities consume about 7.5 million acre-feet per year. If California realized its unique potential to invest in new water supply projects, with federal help, it would give it the ability to be flexible when asserting its senior water rights on the Colorado River. What follows are ways California, and only California, has the potential to increase its annual water yield by 10 million acre-feet per year. That increase would be enough to cope with a prolonged drought without starving cities or farms of water. It would also be enough for California to agree to generous deals with the other states that need water from the Colorado River.
Thin the Water-Guzzling Overcrowded Forests
This is a solution that can be profitably handled by the private sector. Thin the forests on the entire Sacramento–San Joaquin watershed to historically normal levels. As it is, a century of putting out natural fires, along with the regulatory demolition of California’s logging industry, has left forests unhealthy and grown to about five times their normal tree density. The extremely thick tree canopy that results collects snow that evaporates instead of falling to the earth to percolate and recharge the springs that feed mountain streams. The rain and snow that do hit the ground are immediately consumed by the many stressed trees that are competing for an inadequate supply of water, nutrients, and sunlight. Attempts to quantify this impact have reached encouraging conclusions about the extent of the additional water supply potential that forest thinning could deliver.
A fascinating 2011 study by experts from UC Merced, UC Berkeley, and the Environmental Defense Fund reported that 60 percent of the water consumed by the state comes in the form of Sierra runoff, and that when forest cover is reduced by 40 percent, total runoff increases by an estimated 9 percent. As previously noted, California’s water consumption for urban and agricultural use, but not for diversions to maintain ecosystem health, is around 40 million acre-feet per year. That means that if California’s forests were thinned appropriately, 2.2 million acre-feet of water would be added to California’s water supply in an average year.
Doing this would require restoring California’s timber industry, which has withered to a quarter of the capacity it had as recently as the 1990s, thanks to misguided environmentalist restrictions that have done more harm than good. Bringing logging back would create jobs, generate tax revenue, increase the supply and lower the price of lumber, and lower the risk of catastrophic fires.
Dredge the Silt out of the Delta and Delta Tributaries
Ever since the Californian delta levees were constructed over a century ago, and islands and channels replaced a vast marshland, local agencies and private landowners routinely dredged the channels and maintained the levees to preserve navigation and prevent flooding. But, starting in the 1970s, two things happened. First, the State Water Project and the federally owned Central Valley Project were pumping millions of acre-feet every year out of the delta and into aqueducts to serve farms and cities in the San Joaquin Valley and Southern California. Second, and less discussed in terms of the impact it has had, is that with only a few exceptions, regular dredging ceased.
Resuming regular dredging operations along at least 75 miles of south delta channels, along with at least 25 miles of delta tributaries where silt has created flood risk, would have two water supply benefits. First, it would allow at least another million acre-feet per year to be retained in California’s reservoirs. As it is, water is released from these reservoirs to reserve flood control capacity for a strong late spring storm or an abrupt melting of the snowpack. But if the maximum rate of flow in the tributaries and delta channels were increased through dredging, it would be safe to fill reservoirs to higher levels. This would be especially beneficial in dry years when the reservoirs are partially emptied and there are no spring storms or significant snowpack. Dredging would also increase the overall volume of water in the delta, meaning that operating the delta pumps would not as readily alter, or even reverse, the flow of fresh water through the delta. Dredging would also benefit salmon, which prefer to migrate in deeper and cooler water, and help them avoid bass, which prefer warm and shallow water.
Rewrite the Rules Governing the Delta Pumps
The pumps situated at the southern end of the Sacramento–San Joaquin Delta — state and federal combined — have the capacity to move more than 900,000 acre-feet of water per month, but they rarely operate at capacity. According to data provided by the California Department of Water Resources, during the four months between December 1, 2022, and March 31, 2023, 15.8 million acre-feet flowed into the delta, but of that only 1.8 million acre-feet (or 12 percent) were pumped into the Delta Mendota Canal and California Aqueduct, which is only 50 percent of the capacity of the state and federal pumps. During the same four months in 2023–24, another extremely wet year, 12.2 million acre-feet flowed into the delta, and only 1.3 million acre-feet (11 percent) were pumped south: only 37 percent of pump capacity. Over the most recent four wet months, December 2024 through March 2025, 12.3 million acre-feet has flowed through the delta, and of that, only 1.5 million (11 percent) were pumped south: only 40 percent of capacity.
These minimal allocations make even less sense when compared with higher levels of pumping during the preceding drought years. From December 2019 through March 2020, 34 percent of the Delta inflow was pumped south. From December 2020 through March 2021, 24 percent; and from December 2021 through March 2022, 19 percent.
Why, during wet years, aren’t we using more pump capacity to take the so-called big gulp? Expect massive changes by the Bureau of Reclamation and, hopefully, from state agencies under new pressure from a governor who wants to burnish his centrist bona fides in advance of the 2028 primaries. With just modest modifications to the operating restrictions, and using existing pumps, at least another million acre-feet per year can be pumped south from the delta into the state and federal canals.
Build New Infrastructure to Harvest Delta Flows
According to estimates provided in a 2017 report published by the prestigious Public Policy Research Institute, in an average year, over 10 million acre-feet of water flow into the San Francisco Bay from the Sacramento–San Joaquin Delta in excess of what is required for ecosystem health. There are many ways to divert more of this water beyond what could be realized from dredging and higher utilization of the existing state and federal delta pumps. The proposal currently preoccupying California’s water agencies is the so-called Delta Conveyance. This 45-mile-long tunnel, with a 36-foot internal diameter, if it is ever built, would have the capacity to move up to 4 million acre-feet per year from the Sacramento River north of the delta safely under the fragile delta ecosystem, emerging at the southern end of the delta to deliver water to southbound aqueducts. But perpetual, year-round operation would not be possible. The state’s own estimate of the tunnel’s eventual throughput is only 500,000 acre-feet per year, with a construction cost officially (and optimistically) estimated at $20 billion.
While the delta tunnel project dominates water policy debates in California, there are other ways to get more water out when storm runoff surges through the delta. The half-built Folsom South Canal diverts water from the American River, a major delta tributary, transporting it 20 miles south to urban and agricultural users along its course. But this canal could be extended another 25 miles to reach the Clifton Court Forebay, where water from the delta already supplies the existing delta pumps. This longer canal could also tap additional delta tributaries. This underused canal has a capacity of 3,500 cubic feet per second, which is 2.5 million acre-feet per year. If it was extended and connected to additional delta tributaries, it could probably deliver another million acre-feet per year to the delta pumps.
There is also a proposal for fish-friendly delta diversions, an example of potentially game-changing infrastructure. It would involve creating a channel in an existing delta island, lining the bottom, and burying perforated pipes underneath a bed of gravel to withdraw fresh water during storms. With no impact to either current or fish, a 200-acre site could yield 15,000 acre-feet per day. Even if it only operated for 100 days per year, during the wettest months, this project could cost-effectively harvest 1.5 million acre-feet per year from the delta.
Expand Reservoir Storage Capacity
California’s total reservoir storage capacity is not quite 50 million acre-feet. But total capacity is misleading. Most of California’s reservoirs have to leave room to absorb surges in runoff to prevent downstream flooding, so they’re not totally filled. They also have to retain enough water to preserve flow and, in many cases, to generate hydroelectricity, preventing them from being totally emptied. Storage in reservoirs is also often reserved for environmental releases to protect downstream fish habitat, which reduces their yield. But increasing the capacity of reservoirs by raising the height of the dams would generate higher yields, since these existing reservoirs are already meeting their environmental-release and flood-control obligations.
The most promising opportunity is to raise the height of the Shasta Dam. An 18-foot increase would increase the storage capacity of this massive, 4.5 million acre-foot reservoir by another 600,000 acre-feet. At an estimated cost of $1.8 billion, this project is California’s most cost-effective potential reservoir upgrade. Having additional cold water available for summertime releases from a deep pool reservoir like Shasta would also improve downstream habitat. Expanding this reservoir, however, is fraught with controversy. All water projects in California attract organized and apoplectic opposition from well-funded environmentalist litigators and lobbyists, and Shasta’s proposed expansion is no exception.
A major storage project with a slightly greater chance of completion is the Sites Reservoir. This proposed 1.5 million acre-foot reservoir would be north of the delta, an off-stream reservoir designed to store water collected and pumped into it from the Sacramento River during high winter flows. At its latest projected construction cost of $4 billion, the Sites Reservoir is the only major reservoir proposal in California that still has official, if tepid, support from the state legislature and water bureaucracies. On the drawing board since the 1950s, and supposedly funded via a voter-approved water bond in 2014, Sites remains mired in litigation, and it is anybody’s guess if it will ever be built.
Other surface storage projects in various stages of bureaucratic, litigious, or regulatory denial include the Temperance Flat Reservoir, the Pacheco Reservoir, the Del Puerto Canyon Reservoir, the Los Vaqueros Reservoir expansion, and, of course, the legendary Auburn Dam, a massive project that almost got underway in the early 1970s before the culture changed. Expanding surface storage in California is a practical option, offering additional protection against floods, additional options for maintaining environmental flows, and hydroelectric power. But even the most rational, most environmentally friendly proposals are fiercely opposed by greens and their allies. Unless the regulatory and legal landscape is completely restructured, expanding surface storage in California will be painfully slow and extremely costly. But there are other ways to store water.
Expand Underground Storage Capacity
California is blessed with capacious aquifers so vast that the extent of their capacity remains unknown. An expert assessment from Stanford University puts the range between 850 million and 1.3 billion acre-feet. This is a staggering amount of available storage, most of it situated in the San Joaquin Valley south of the delta. It would make a tremendous staging area to store water, not only for the nearly 5 million acres of irrigated farmland in the San Joaquin Valley but also to supply the 25 million Californians who live in the major metropolitan areas of greater Los Angeles and San Diego.
The drawbacks to underground storage are the necessity to identify and avoid (or remediate) contaminated aquifers, the energy required to pump the water back out of storage, and the challenge of managing how much water drawn out of the aquifer goes back to the purchaser that put the water into it. Unlike water contained in a reservoir, water in aquifers drifts, and a percolation basin in one county may end up recharging the wells in an adjacent county. But this is not enough downside to diminish the opportunity.
As it is, farmers throughout the San Joaquin Valley already have distribution canals through which they receive irrigation water allocated each year from the state’s California Aqueduct and the federally operated Delta-Mendota Canal. With their groundwater pumping now restricted because of dangerously depleted aquifers, they have the opportunity to allocate a portion of their acreage to creating percolation basins connected to the existing systems built to receive water from the aqueducts. Then, if more water is withdrawn from the delta through new projects or increased pumping, they can receive water deliveries in winter and store it underground.
On the eastern side of the San Joaquin Valley, farmers can also reserve Sierra runoff to recharge their aquifers. From storm runoff in January to snowmelt in June, diverting water when rivers are running high is a cost-effective way to recharge aquifers. Apart from aqueduct deliveries, the total runoff into the San Joaquin Valley that isn’t, but could be, harvested for recharge is estimated at 700,000 to 900,000 acre-feet per year.
And then there are the “paleochannels,” formed during the ice age when the sea level was about 400 feet lower than it is today. These ancient rivers slowly rose as the oceans rose to their current elevation and now form underground canyons loosely filled with rock and gravel, capable of absorbing rapid infusions of water. We now have technologies capable of pinpointing where these underground caverns are located, and we are close to being able to make practical use of them for storage. The promise of paleochannels is rapid recharge, which would enable floodwater that might overwhelm conventional percolation basins to be stored underground as fast as it comes down the river.
Urban Wastewater Reuse, Runoff-Harvesting, and Desalination
California’s massive coastal cities, all of them situated on semiarid landscapes, have long relied on imported water from the California Aqueduct, the Colorado River Aqueduct, the Los Angeles Aqueduct, and the Hetch Hetchy Aqueduct, which together deliver millions of acre-feet every year. But that requirement is slowly diminishing as these cities develop more capacity to harvest runoff from winter storms, from recycling and reusing their wastewater, and from desalination.
A 2022 study by the Pacific Institute concluded that California’s urban “stormwater capture potential is 580,000 AFY [acre-feet per year] in a dry year to as much as 3.0 million AFY in a wet year.” The challenge, of course, is whether engineers can design systems to capture whatever the skies deliver. In Los Angeles, average annual rainfall is only 12 inches per year, but on August 20, 2023, 2.5 inches fell within 24 hours, nearly all of it running into the Los Angeles River. Building the infrastructure to harvest that occasional torrent would be like building a 50-lane freeway to keep traffic moving at the speed limit during an unusually heavy rush hour. It makes no sense. But throughout Los Angeles County and elsewhere, cities are investing in daylighting streams and reducing impermeable surfaces to encourage percolation, in addition to building dedicated percolation basins. It’s making a difference. In the very wet 2022–23 rainy season, L.A. County Public Works estimated that stormwater capture at groundwater recharge facilities totaled over 500,000 acre-feet.
California’s cities are slowly upgrading their wastewater recycling and reuse infrastructure, with Orange County now reusing 100 percent of its wastewater. Lagging at the other end of the adoption spectrum are the 37 wastewater plants surrounding the San Francisco Bay, which continue to release over 400,000 acre-feet per year of nutrient-rich, inadequately treated water. Not only is this water not captured for reuse, the discharge nourishes algae blooms that die and turn toxic, with devastating effects on the San Francisco Bay ecosystems. Wastewater recycling is expensive, but the alternative is restoring the ecosystems where wastewater is currently released and finding another source of fresh water. In the event of a prolonged drought, or some other crisis that disrupts water imports, having the ability to reuse wastewater might make the difference between hardship and catastrophe.
Which brings us to desalination. Contrary to the perception spread by its opponents, desalination is cost-effective, energy-efficient, and can be deployed at a massive scale. The Rabigh 3 Independent Water Plant in Saudi Arabia, for example, produces an impressive 175,000 acre-feet of fresh water per year. The Ashkelon Desalination Plant in Israel produces 120,000 acre-feet of fresh water per year. Total worldwide desalination capacity is estimated to be 28 million acre-feet per year. There is no reason why California, where a strong offshore current can dissipate the brine, should not have world-leading desalination capacity along the Southern California coast. As for energy consumption, if the 2 gigawatts of power generated by the Diablo Canyon nuclear power plant, for example, were used for desalination, it would be enough to produce 5 million acre-feet of fresh water per year. Desalination is a huge opportunity. California’s hesitancy to embrace this technology ignores our need for a resilient and diverse water supply and showcases the paralysis brought about by excessive regulation and relentless lawfare.
Given the potential of urban runoff-harvesting, wastewater reuse, and desalination, we must not underestimate just how much water supply can be locally generated within California’s densely populated cities. Through a combination of all three of these project types, it is feasible to add another 2 million acre-feet per year, if not more, to California’s total water supply.
While some of these projects may overlap, it is safe to estimate the potential of new water supply projects to deliver the following: forest-thinning, 2 million acre-feet per year; dredging delta channels and tributaries, 1 million acre-feet per year; restructured delta pumping rules and new facilities to safely divert flood runoff from the delta, at least 3 million acre-feet per year; expanded surface storage, 1 million acre-feet per year; runoff-harvesting from Sierra tributaries, 1 million acre-feet per year; urban runoff-harvesting and wastewater reuse and desalination, at least 2 million acre-feet per year.
It may be that some of these options do not offer sufficient benefit to justify the cost. But in California’s current political and regulatory environment, none are cost-effective. And in an appropriately streamlined, aggressively maintained deregulated environment, all could make economic sense. How our politicians navigate this issue will determine which of these projects ever see the light of day, but there are some encouraging signs. Trump seems set on helping Californians enjoy the water abundance that should be theirs, and Governor Gavin Newsom’s potential national political ambitions may lead him to conclude that a little less obstructionism would be helpful.
One thing is certain. California is the only state in the American Southwest that has the ability to develop another 10 million acre-feet of reliable water supply per year. Unlike in every other state, where options are severely limited by geography and climate, in California, it is a political choice.
This article originally appeared in National Review.
Edward Ring is the director of water and energy policy for the California Policy Center, which he co-founded in 2013 and served as its first president. He is also a senior fellow with the Center for American Greatness, and a regular contributor to the California Globe. His work has appeared in the Los Angeles Times, the Wall Street Journal, the Economist, National Review, City Journal, and other media outlets.