How Deep Sea Water is Now Drinkable

Author: Matt Ferrell

Freshwater may soon flow from the depths of the ocean to drought-stricken coastal cities. A handful of companies are betting that crushing deep-sea pressures can replace the energy-hungry pumps and toxic chemicals that are desalination’s inconvenient truth. By going the extra quarter-mile into the ocean, they’re pioneering a way to turn saltwater into freshwater — slashing costs, curbing pollution, and reducing environmental harm in the process. How on earth…or, under earth…does this work? And could it solve our global water crisis?

A handful of companies are looking to replace the pump-driven pressure of a reverse osmosis (RO) desalination system with deep-sea pressures, using 400 meters (or more than 1,300 feet) of hydrostatic pressure as an alternative energy source to powering those pumps with fossil fuels. You know that pain in your ears when you dive to the bottom of a swimming pool? Now multiply that by a hundred. That’s the kind of force these companies are harnessing. They plan to install entire farms of desalination pods on the seafloor, like these 13 meter (or 40 foot) tall pods designed by OceanWell in California.¹ Before getting into how exactly they’re doing this, there’s the question of why? Why dive to these depths when we can already do RO onshore?

Well, the southwestern U.S. is suffering from drought so severe that Lake Mead, the largest reservoir in the Colorado River Basin, has 150-foot-tall bathtub rings around its edges marking where water levels stood just a few decades ago.² 40 million people in seven states rely on the Colorado River, but the lands it flows through are the driest they’ve been in 1,200 years.³ The water crisis is reshaping daily life: stalling hydropower plants, triggering citywide water-restrictions, and driving farmers to abandon their fields.⁴⁵

History is full of civilizations brought to their knees by water shortages. The Ancestral Puebloans abandoned their massive cliff dwellings in the American Southwest after decades of dry years.⁶ A megadrought helped topple the Ming Dynasty in China.⁷ And the Dust Bowl of the 1930s saw much of the Great Plains become unlivable wasteland.⁸

But whereas these droughts lasted less than 20 years each, the Southwest is in its 25th year with no end in sight. Earth’s climate is changing, and multi-year droughts are becoming more frequent, more severe, and more expansive as they continue to spread. Each year, an additional area the size of Vermont and New Hampshire combined succumbs to drought.⁹¹⁰¹¹ Yet global populations keep growing and urbanizing, placing even greater demands on limited water supplies.¹²

The question is: water we going to do about it?

Saltwater, Hold the Salt

What we’re doing right now works, but has its challenges. For instance, on California’s coast, the Carlsbad Desalination Plant is stepping in where the Colorado River is falling short, turning saltwater into freshwater to cover 7% of San Diego County’s needs.¹³ It’s part of a growing global trend: desalinating seawater and brackish water to supply freshwater for drinking, industry, and even agriculture.

In 2024, roughly 21,000 desalination plants operated across roughly 150 countries, from the United States to Southeast Asia, with half of the world’s desalination capacity located in the Middle East and North Africa.¹⁴ More than three-quarters of these plants use a technique called reverse osmosis, or RO.¹⁵

RO forces saltwater against a membrane with microscopic pores that let water molecules through but hold back the larger salts, as well as microbes and chemical contaminants. It sounds like a simple solution, but RO comes with some major complications.

The first is that it requires massive amounts of energy. RO relies on powerful pumps to brute force water through a membrane, and that takes a lot of electricity: about 3kWh per cubic meter or 260 gallons.¹⁶ Back in 2016, global desalination capacity stood at 38 billion cubic meters per year (BCM/y), consuming roughly 75 terawatt-hours (TWh) of electricity — as much as the entire country of Chile used that same year! ¹⁷ And with freshwater demand rising, capacity is expected to more than double by 2050.¹⁸

But with great power comes great emissions. RO plants rely almost entirely on fossil fuels, making desalination a major source of CO2, nitrogen and sulfur dioxides, and small particulates. In 2016 alone, desalination plants emitted 76 million tonnes of CO2, a number expected to surge to 218 million tons per year by 2040.¹⁹

The obvious solution would be to turn to renewable energy. The world’s first large-scale RO plant powered by solar panels was completed in Saudi Arabia in 2018 with enough capacity for 150,000 people.¹⁴ But at night, when the sun goes down, the plant’s environmental impact goes up as it switches to grid power.²⁰

When we can’t use the sun, where do we find a 100% sustainable, round-the-clock power source? Look no further than OceanWell’s desalinating pods in the depths of the ocean.

Deep-Sea Reverse Osmosis

This is where we come back to OceanWell’s 13-meter pods desalinating water on the ocean floor. The idea of deep-sea RO (DSRO) is as old as RO itself. But back in the 1960s, the thought of installing and powering pumps at depth was just a bit too “far out.”²¹²² Today, that’s no longer the case. At places like the Ormen Lange gas field off Norway’s coast, wellheads on the seafloor connect to a shared subsea hub that supplies electricity and pumps gas ashore through a pipeline.²³ It’s the same hub-and-spoke model now being proposed for deep-sea desalination.

This all works because companies like Norway’s FSubsea AS have developed pumps that both stay watertight at extraordinary depths and rarely need maintenance.²³²⁴ Also headquartered in Norway, Flocean is a direct spin-off of FSubsea, taking technology originally designed to extract fossil fuels and repurposing it to pull freshwater from the ocean more sustainably.²⁵

This is still reverse osmosis, but about 40% more energy efficient at only 1.7-2.1kWh per cubic meter of freshwater.²⁶²⁵ That’s because instead of building pressure against the saltwater side of the membrane, deep-sea RO pumps get a much easier task: creating suction on the freshwater side to keep water flowing through and moving towards shore.²⁷²⁵

Beyond these energy and cost savings, another Norwegian company, Waterise, expects that moving RO offshore will shrink the land area needed by 80 to 95%.²⁸²⁹ That’s crucial in urban areas like Los Angeles, where OceanWell is partnering with the Las Virgenes Municipal Water District to build its first deep-sea water farm.³⁰ Space is also at a premium along the built-up shores of the Mediterranean and on the tiny island nation of the Maldives, two locations that Flocean is targeting for its own deep-sea RO pods.²²

While deep-sea RO doesn’t need much land, it does need depth: 300 to 600 meters of it, or about 1,000 to 2,000 feet. To reach that, Flocean says its RO pods will sit up to 6 miles or 10 kilometers offshore.³¹³² That means miles of pipelines to shore and long, expensive umbilical cables to deliver power to the pumps, which is one reason deep-sea RO has to be done at scale to be cost-effective.²⁷ But OceanWell’s CTO Michael Porter imagines a time when these underwater RO farms run on offshore wind. Instead of relying on the grid, they’d pull power from turbines spinning nearby, cutting costs and reducing their onshore footprint even more.²⁷

If you’re questioning the environmental impact of putting RO pods on the seafloor, consider the alternative…because traditional RO has a serious sustainability problem. Land-based RO burns through huge amounts of energy to pressurize water against a membrane. That means plants have an economic incentive to squeeze out as much freshwater as possible. 58% of their intake water goes back into the ocean, carrying 100% of the original salts. That’s a doubly salty brine, not even mentioning the chemical cocktail used to pretreat seawater before it even reached the membrane.¹⁸ This heavy brine sinks to the seafloor, stressing fish and other sea creatures that aren’t adapted to such extreme salinities. And as water gets saltier, it holds less oxygen, suffocating life on the seabed.³³¹⁸

This is a massive problem. Over 155 million tons of brine get dumped in the ocean every single day.⁵ Some plants blast brine into coastal waters to mix it more thoroughly, while others trickle it along the shoreline or dilute it with other wastewater discharges.³³

But instead of just managing brine, deep-sea RO disperses it altogether. Because deep-sea pressures are unlimited, there’s no pressure to squeeze every last drop of freshwater out of saltwater the way land-based RO plants do. OceanWell claims that its system merely sips saltwater, returning 85-95% of it back to the ocean with only a slight increase in salinity.²⁷ To keep brine from settling on the seafloor or drifting back into the intake, OceanWell’s pods pump it higher into the water column, where currents carry it away.³⁴²⁷

And those nasty pre-treatment chemicals I just mentioned? Deep-sea RO dodges them entirely, thanks to one key difference from land-based systems. RO membranes clog easily from microorganisms in seawater and mineral buildup. To prevent this, land-based RO plants pre-filter seawater with plastic-based filters. Then, they add biocides like chlorine to kill microbes. But because chlorine damages RO membranes, it has to be neutralized with yet another chemical: bisulfite. Treating the treatment. More chemicals adjust the water’s pH, and scale inhibitors keep minerals like carbonate and phosphate from clogging pipes.¹⁶ It all adds up.

But deep-sea RO pares it back down. These RO pods sit in the perpetual darkness of the ocean’s “twilight zone,” where algae don’t grow and oxygen levels stay low. With so little life at these depths, Flocean and OceanWell expect the membranes to stay clean without chemical treatment.²⁸²⁵³⁴

Even so, OceanWell is taking extra steps to protect what little life exists at these depths. The company is developing an intake system that draws seawater through a series of increasingly finer filters and flushes out any marine life trapped along the way. This “catch and release” method is designed to return plankton and larvae to the ecosystem while also keeping the filters clear and reducing membrane fouling to keep the pods running maintenance-free for as long as possible.³⁵²⁷²²

That said, there’s yet another sustainability leak deep-sea RO hasn’t plugged. Even with all these safeguards, RO membranes don’t last forever. They’re still consumables that need replacing every 5 to 10 years. A 2016 study estimated that 14,000 tonnes of discarded membranes end up in landfills each year — a number that has only grown as RO desalination has expanded.³⁶

So what happens when the system eventually clogs up…and how would they even know? OceanWell says the same umbilical cord that supplies power from shore will send data back from sensors on each pod. These sensors will allow OceanWell to monitor performance in real time and shut down individual pods as needed, until they can be swapped out for fresh ones.²⁷

For now, Oceanwell is focused on perfecting its filtration system in hopes of maintenance-free pods. It plans to launch a pilot in 2026, with its first commercial plant serving Los Angeles by 2028. The facility is expected to produce 95,000 cubic meters or 25 million gallons per day — that’s 28,000 acre-feet per year. Double that to a full scale farm, and it could supply enough freshwater for a small city.²⁷³⁴

And if you’re wondering whether replacing pods in pitch-black darkness under crushing pressures a quarter-mile deep is complicated…it definitely is.

A Race to the Bottom

But, with decades of subsea experience, Flocean and Waterise are already lowering RO systems onto the seabed.³⁷ Flocean recently wrapped up a 4-month pilot demonstration at depth and is now preparing to launch a 1000 m³/day (or 260,000 gallon) commercial demonstration.³⁸ So, we may be close to having freshwater on tap…from the abyss.

The age of desalination is here, and the challenge now is making it in an efficient and sustainable way. Deep-sea RO promises to deliver on both, but while it might keep coastal communities afloat, inland regions will still be left high and dry. And to truly secure water in the face of worsening droughts, we can’t just make more: we need to make the most of what we do have. That means conserving water, treating and reusing wastewater, and making every drop count.