Some four miles off the Southern California coast, a company is betting it can improve desalination by moving the process deep beneath the ocean’s surface, where it would draw on natural ocean pressure. OceanWell’s planned “Water Farm 1” would use reverse osmosis pods that force seawater through membranes to filter out salt and other impurities, the company said.
OceanWell said the system is designed to be located about 1,300 feet (400 meters) below the water’s surface and would produce up to 60 million gallons (nearly 225 million liters) of freshwater daily. The company also said that its deep-sea approach would cut energy use by about 40% compared with conventional plants.
In addition to energy, OceanWell said it is targeting other drawbacks associated with standard desalination. The AP described desalination as energy intensive and said desalination plants worldwide produce between 500 million and 850 million tons of carbon emissions annually, approaching about 880 million tons emitted by the entire global aviation industry. The AP also said traditional desalination can worsen environmental impacts through highly concentrated brine discharge and through seawater intake systems that can trap and kill fish larvae, plankton and other organisms at the base of the marine food web.
OceanWell CEO Robert Bergstrom said: “The freshwater future of the world is going to come from the ocean,” and “we’re not going to ask the ocean to pay for it.” The plan is being advanced as drought, changing rainfall patterns and wildfires push more regions to seek new drinking-water supplies, including from the sea.
OceanWell’s test and development are not limited to Southern California. The company has signed an agreement to test its system in Nice, France beginning this year, and it is already testing a prototype in the Las Virgenes Reservoir with the local water district. OceanWell said that if its approach works, reverse osmosis pods would eventually float above the sea floor in Santa Monica Bay, anchored with a minimal concrete footprint, while an underwater pipeline would carry freshwater to shore.
The company said its design would use screens intended to keep out even microscopic plankton and would aim to produce less concentrated brine discharge. Gregory Pierce, director of UCLA’s Water Resources Group, said deep sea desalination appears promising from an environmental and technical standpoint, but he said the real test will be cost. Pierce said: “It’s almost always much higher than you project” and “So that, I think, will be the make or break for the technology.”
Pierce’s warning points to a challenge facing the technology as it scales: the article notes that Las Virgenes Reservoir serves about 70,000 residents in western Los Angeles County and that nearly all the water originates in the northern Sierra Nevada and is pumped some 400 miles (640 kilometers). When low rainfall and snowpack reduce supplies, the reservoir and communities it serves can face shortages.
While OceanWell is developing its deep-sea approach, desalination already has a major footprint in California. About 100 miles (160 kilometers) down the coast, the Carlsbad Desalination Plant came online in 2015 and can produce up to 54 million gallons (204 million liters) of drinking water daily. The AP said the plant supplies about 10% of San Diego County’s water, enough for roughly 400,000 households, and positioned it as a locally drought-proof water source drawn from the Pacific Ocean.
But the AP described an ongoing debate over desalination’s environmental tradeoffs. The AP said environmental groups have argued the plant’s seawater intake and brine discharge pose risks to marine life, and that its high energy demands can drive up water bills and worsen climate change. Patrick McDonough, a senior attorney with San Diego Coastkeeper, said the plant “sucks in a tremendous amount of water, and with that, sea life,” adding: “We’re not just talking fish, turtles, birds, but larvae and spores — entire ecosystems.”
The AP said a 2009 Regional Water Quality Control Board order estimated the plant would entrap some 10 pounds (4.5 kilograms) of fish daily and required offsetting those impacts by restoring wetlands elsewhere, and it said that restoration remained incomplete after 17 years. It also said a 2019 study found the plant’s brine discharge raises offshore salinity above permitted levels, though it detected no significant biological changes.
Michelle Peters, the chief executive officer of Channelside Water Resources, which owns the plant, said the facility uses large organism exclusion devices and one-millimeter screens to minimize marine life uptake, while acknowledging some smaller species can still pass through. Peters said the plant dilutes its brine discharge with additional seawater before releasing it back into the ocean and that years of monitoring have shown no measurable impacts to surrounding marine life, and she said the Carlsbad plant has significantly cut its energy consumption through efficiency improvements and operates under a plan aimed at making the facility carbon net-neutral.
Many experts cited in the article said water recycling and conservation should come first, noting that wastewater purification typically uses far less energy than seawater desalination and can substantially reduce impacts on marine life. The AP said Las Virgenes is pursuing a wastewater reuse project alongside its desalination partnership, and that Las Virgenes’ Pedersen said: “What we are looking for is a water supply that we can count on when Mother Nature does not deliver,” and “Developing new sources of local water is really a critical measure to be more drought and climate ready.”