Can California Drink the Pacific? The Promise and Problems of Desalination
California’s Carlsbad plant turns 100 million gallons of seawater a day into drinking water. How desalination works, why it’s so expensive and where new plants are planned.
Updated
Andrew Innerarity / California Department of Water Resources.
Water, water, every where, nor any drop to drink.
_— Samuel Taylor Coleridge’s poem The Rime of the Ancient Mariner. _
California has about 850 miles of coastline and a chronic shortage of fresh water. So why not just drink the ocean? That’s the idea behind desalination, and in California it’s slowly going from a fringe idea to part of the plan.
The mission of the Seawater Desalination Test Facility in Port Hueneme, Ventura. John Chacon / California Department of Water Resources
California has always had droughts, and some of its driest years on record have been recent ones. Climate change is making the snowpack and reservoirs less reliable. Big storms in 2023, 2024 and 2025 eased things for now, but plenty of experts expect serious drought to come back and become the new norm.
So desalination plants are starting to pop up along the coast. The biggest is the Claude “Bud” Lewis Carlsbad Desalination Plant in San Diego County, the largest in the Western Hemisphere.
Every day it takes in about 100 million gallons of seawater and turns half of it into drinking water, about 50 million gallons. Since opening in 2015, it has supplied roughly 10 percent of the water used by San Diego County’s 3 million-plus residents. The catch: that water costs nearly twice as much as the region’s other main sources.
Claude “Bud” Lewis Carlsbad Desalination Plant (Photo courtesy of Carlsbad Desalination Project)
Most California plants use reverse osmosis. Normally, through osmosis, water moves across a membrane from the less salty side to the saltier side. Reverse osmosis uses brute force to push it the other way. Seawater is pumped at very high pressure against a membrane that lets water molecules through but blocks salt and most other impurities.
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That takes a lot of energy. Reverse osmosis needs pressure far higher than seawater’s natural osmotic pressure, and then there’s the maintenance and the salty brine left over. Energy is the main reason desalinated water is so expensive, and if the power comes from fossil fuels, it’s not great for the climate either.
John Chacon / California Department of Water Resources
The membranes themselves are impressive. They’re usually a very thin film of polyamide, a type of plastic, engineered so water molecules can squeeze through while salt can’t.
Besides the energy, there’s the brine. For every gallon of fresh water, there’s a gallon of extra-salty water left over, and when it’s dumped back into the ocean, it has to be diluted carefully so it doesn’t harm sea life. Intakes can also suck in fish larvae and plankton.
Charles E. Meyer Desalination Plant in Santa Barbara, California, plays a key role in improving water reliability and resiliency during the drought years. Florence Low / California Department of Water Resources.
Engineers are working on all of that. Forward osmosis uses natural osmotic pressure instead of pumps, plants can run on solar and wind power, and researchers are designing biomimetic membranes modeled on nature’s own filters, like mangrove roots and animal kidneys.
More plants are in the works. The Doheny Ocean Desalination Project in Dana Point has gotten more expensive but, at last report, was still moving ahead, with completion expected around 2027. It would supply about 5 million gallons a day to south Orange County.
In November 2022, the California Coastal Commission approved a permit for Monterey Bay Area Desalination Plant, a $330 million plant proposed by California American Water in Marina, a working-class city of about 22,500 people roughly 15 minutes north of wealthier Monterey. It would produce 4.8 million gallons a day.
Monterey Bay at Moss Landing, California. Photo: Erik Olsen
Marina’s mayor, Bruce Delgado, opposed it. His argument: Marina would get the industrial plant and the environmental damage, while richer places like Carmel-by-the-Sea, Pacific Grove and Pebble Beach got the water. It’s a good example of how desalination isn’t just an engineering question.
The state is also looking inland. In February 2024, the California Department of Water Resources identified future projects to desalinate brackish groundwater, which is less salty than seawater and cheaper to treat. The goal, from California’s Water Supply Strategy: Adapting to a Hotter, Drier Future, is 28,000 acre-feet a year of new brackish desalination by 2030 and 84,000 by 2040.
The state’s water plan leaves room for more desalination, especially in coastal cities that are short on water.
Desalination won’t fix California’s water problems on its own. It’s expensive, energy-hungry and hard on the ocean. But as droughts get worse, a reliable supply that doesn’t depend on snow or rain is looking more and more worth the price. Coleridge’s sailor was surrounded by water with nothing to drink. California would rather not end up in the same boat.
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