Could ocean-floor filtration pods create drinking water?


October 20, 2023

A Californian start-up is investigating the feasibility of harvesting freshwater from desalination pods on the ocean floor.

OceanWell is partnering with Las Virgenes Municipal Water District (LVMWD) in southern California to pilot the state’s first "blue water farm". The project will be the first to use OceanWell's purification technology to create a new supply of drinking water.

OceanWell says its technology has the potential to turn any raw water source into drinking water, without the environmental impacts of traditional desalination methods, which is energy intensive and creates a brine byproduct that can harm eco-systems.

"After seven years of research and technological development, we are proud to present a sustainable, reliable and environmentally friendly source of fresh water." Robert Bergstrom, OceanWell

The collaboration comes as southern California recovers from years of record-breaking drought. To minimise future climate change impacts, LVMWD is exploring innovative solutions to create local water resources and reduce dependence on imported supplies.

David Pedersen, LVMWD general manager, "We are excited to embark on this cutting-edge initiative with OceanWell.

"Providing clean, healthy and consistent water to our customers is the most important function of our water utility. Researching new technology can help us to ensure a more sustainable and reliable water future."

OceanWell's purification pods use water pressure to drive the reverse osmosis process, which separates water from salt. By placing the pods at depths of up to 426m, natural water pressure will help power the filtration process, using up to 40% less energy than conventional desalination.

Pods at depths of up to 426m will deliver purified drinking water. Image: OceanWell

OceanWell estimates it can make around 38 million litres of fresh water every day. It says the system is low energy, scalable and minimises the need for onshore facilities, while protecting marine life.

Robert Bergstrom, OceanWell's founder, said, "The collaboration with LVMWD is a major milestone in our 'environment first' strategy, aiming to bring OceanWell water farms to California municipal water systems. After seven years of research and technological development, we are proud to present OceanWell as a sustainable, reliable and environmentally friendly source of fresh water."

LVMWD serves more than 75,000 residents in the cities of Agoura Hills, Calabasas, Hidden Hills, Westlake Village and areas of western Los Angeles County. The pilot project will be undertaken in the district’s Las Virgenes Reservoir in the City of Westlake Village.


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How is the OceanWell process different from current desalination methods?

Desalination is a heavy industrial process, as it is currently practiced, that removes seawater (including small organisms) from the oceans for processing on land, filters out and disposes of those organisms and other impurities in landfills, either evaporates or pressurizes the filtered seawater, squeezes out as much fresh water as technically possible, and then disposes of a doubly-salty brine back into the sea where it can be toxic.

The Ocean Well uses a passive process driven by natural forces to harvest fresh water from the relatively lifeless deep sea:

It does not kill small organisms with chemicals. It uses the same reverse osmosis membranes as onshore desalination plants, but allows microscopic lifeforms to pass through the process unharmed.

It does not produce toxic brine. The feed seawater is not pressurized and only small amounts of fresh water are extracted, allowing its seawater discharge to stay near ambient pressure and salinity, such that is not toxic in any way. In fact, according to the California Ocean Plan, “discharges shall not exceed a daily maximum of 2.0 parts per thousand (ppt) above natural background salinity measured no further than 100 meters (328 ft) horizontally from each discharge point.” This equates to 5.7% above a 35 ppt background salinity typical in California. The Ocean Well maintains a discharge of only 5% above ambient ocean salinity, thus never producing “brine”.

It does not heat or pressurize the feed seawater. While it does pressurize the harvested fresh water in order to deliver it to shore, there is no marine life in the fresh water and this design cuts pressurization requirements in half, meaning lower energy requirements, lower carbon production, and lower operating costs.

Will the OceanWell help or hurt the earth and oceans?

The Ocean Well was intentionally designed to help the earth and oceans, inspired by the multiple functions of a mangrove root system: Its supports life on earth, using reverse osmosis membrane barriers to lightly draw fresh water from the relatively lifeless deep sea for use on land.It supports life in the oceans, by creating nutrient-rich habitats to feed marine life and subsea infrastructure to power ocean monitoring systems for learning more about the deep sea.

The Ocean Well will help rebalance Earth’s water cycle: As global temperatures rise, the moisture-holding capacity of Earth’s atmosphere increases, and climatological and hydrological patterns change. These changes may cause increases in global precipitation, more concentrated over the oceans than land, leading to increased aridification in many of today’s most habitable regions of Earth, including parts of North America, Eurasia, and Australia. For life as we know it to continue, we need to fix the broken water cycle and rebalance the distribution of our planet’s fresh water supply to sustain life on Earth.

Will it raise the cost of fresh water?

Ocean Well water will cost less, at a large scale, compared to today’s best desalination technologies in locations with deep seawater close to shore. Water prices are rising around the world as “free” sources of fresh water become exhausted: The Ocean Well cannot produce “free” water, but it uses up to 50% less energy per cubic meter produced than seawater desalination.

Depending on location, Ocean Well water may even be priced lower than stormwater capture, recycled wastewater, imported water, brackish desalination, and some conservation efforts. As an added bonus, the Ocean Well produces very cold water that can be used in once-through cooling applications before it’s consumed as drinking water, thus offsetting cooling costs. Synergies with other offshore renewables and climate technologies, such as wind power and carbon capture, may provide opportunities to further cut the cost of fresh water.

Why has this not been done before?

The Ocean Well combines proven technologies from the offshore energy and desalination industries: While the desalination sector has been relatively stagnant since its last major innovation in the late-1990s, the offshore energy sector is relatively young with major innovations in subsea systems occurring in the late-2010s.

The principles behind subsea reverse osmosis were theorized decades ago, but were technically infeasible, until now. Now, because of the development of reliable subsea technologies, the Ocean Well is not only feasible, but offers favorable economies of scale and unprecedented ecological benefits.