Water Supply
California Water Agency Ramps Up Novel Deep-Sea Desalination Plan
Deep-sea desalination envisioned to supply the Las Virgenes Municipal Water District in the Los Angeles area will use "pods" secured in the ocean—simlar to this one being tested in a municipal reservoir—to produce water with up to 40% less energy needed than on-land processes
Los Angeles area water agencies were hard hit in 2022 by successive years of drought and an unprecedented meager State Water Project allocation, but none was more impacted than Las Virgenes Municipal Water District, which serves about 70,000 users in an upscale section of the city with virtually no other supply alternatives, in-state or out. The severe per-person water-use limit prompted officials to come up with a plan to create new supply through a novel in=ocean desalination process.
“We cannot stand idle for a repeat of 2022 when our water supply from [the Metropolitan Water District of Southern California] was reduced by 74%. It was not an anomaly” says David W. Pedersen, water district general manager. But onshore desalination used elsewhere in California is energy intensive and can cause environmental harm—prompting him and other officials to link up with developer OceanWell to test its offshore approach, using cylindrical “pods” placed as deep as 1,400 ft that would rely on ocean pressure to power seawater intake pumps and filters to produce potable fresh water through reverse osmosis. Las Virgenes completed pod testing in a municipal reservoir in late 2025, with funding provided by the Metropolitan Water District and U.S, Bureau of Reclamation.
The nine-month pilot “exceeded expectations,” says Mark Golay, OceanWell director of engineering projects, noting that it “helped us prove” that the underwater reverse osmosis process “is a practical and economic way to reduce the cost, energy, and environmental impact of water treatment applications.” He says the tested pod had recoverable flowrates of 85% over the study period, and 93% operating efficiency. Adds Pedersen: “A number of mitigation strategies were developed and tested during the pilot study to determine the most effective means to clean the pod.”
The goal is to scale to an ocean-based “farm” system of multiple pods about 4.5 miles offshore of Malibu that could produce, when operating by about 2028, up to 50-60 million gallons per day. The effort could cost from $500 million to $1-billion, according to an LA Times estimate. Water would be pumped to shore through one or more landfall pipelines, an effort supported by six other water agencies, says Pedersen.
“We are working to form a joint powers authority to provide a more structured means to work together on this effort and on other water supply and reliability strategies,“ he adds. The agencies also hired engineer HDR to design a conveyance system to move desalinated water to coastal and inland communities using existing and new infrastructure.
Next steps now include an ocean trial set for fall in Santa Monica Bay with a pod suspended at depth from the back of a boat, which has already received approval from the California Coastal Commission and "marks a critical step from controlled reservoir conditions to real-world ocean deployment,” says OceanWell. Also planned is a demonstration project that places a pod in-situ anchored to the ocean floor at depth for about one year to collect data, Pedersen says. “We are preparing feasibility studies on both the onshore and offshore infrastructure that would be required to advance a full-scale project of up to 50 million gallons per day,” he notes, with data supplied to state and federal regulators for permits and to determine if the process is cost effective and competitive.
OceanWell also is exploring new efforts to link up with water agencies in southern France, and also Arizona toi deploy its system—as water agencies in that state, California and Nevada signed an agreement June 3 to explore interstate exchanges involving desalinated and recycled water supplies using existing Colorado River delivery systems. The firm says it aims to build 15 water farms across the globe in the next decade.
In addition, Las Virgenes is investing in potable water reuse to supply 30% of its demand, Pedersen says.
