Sean Bothwell can understand why people think desalination is a silver bullet. When he was a kid living in California’s Orange County, the ocean was always close by. It didn’t make sense to him that all the water near him wasn’t usable.
“I grew up thinking, like, why the heck aren’t we desalinating?” said Bothwell, who is now executive director of the California Coastkeeper Alliance. “Why are people always saying that we need to save water and conserve?”
Now, a few decades later, California is in an even more dire situation—as is the rest of the world, much of which went through one of the driest summers on record last year. As water crises around the world become more common as climate change stresses already-overused water systems, it’s clear more resources are going to be needed. Making use of abundant ocean water seems like a better and better deal.
In California, which had its driest six-month stretch on record last year, high-profile leaders have voiced support for desalination. “We need more tools in the damn tool kit,” Governor Gavin Newsom told the Bay Area News Group editorial board last April, where he was voicing support for a proposed ocean desalination plant in Huntington Beach. But less than a month later, in a unanimous decision, the California Coastal Commission rejected the proposal for the plant Newsom supported: a $1.4 billion project, owned by the Poseidon Water company, that would have produced 50 million gallons of drinking water each day.
The idea of dismissing the Poseidon plant, which could have provided drinking water to 400,000 people a day, during the worst drought in 1,200 years may seem foolish. But experts say that while the idea of simply making salt water potable is alluring, there’s a host of problems with ocean desalination that need to be addressed—and far better tools in the kit Newsom spoke of that we should turn to first. And even if desalination is the best idea for some communities, it has to be considered on a case-to-case basis.
For his part, after doing his graduate school thesis on desalination as an adaptation mechanism for climate change, Bothwell’s mind began to change on the process of ocean desalination, and he finally understood its problems and limitations.
“I realized all the things that people don’t understand about desal—of all the issues we work on, [the efficacy] is the toughest thing to communicate to people,” he said. “Everyone thinks it’s a good idea.”
Humans have been separating salt from ocean water for thousands of years. Minoan sailors probably used the process in their voyages across the Mediterranean Sea as far back as 1300 BCE; descriptions of a specific process sailors used to boil water were recorded by Greek philosopher Alexander of Aphrodisias in 200 CE. In the early days of the U.S., Secretary of State Thomas Jefferson ordered desalination methods to be printed and posted on clearance permits for boats sailing in and out of U.S. ports and recommended that those who try out desalination to make their results public, so “that others may, by their success be encoraged [sic] to make similar trials, and may be benefited by any improvements or new ideas which may occur to them in practice.”
There are currently around 17,000 desalination plants operating in the world, with high concentrations in areas where water is extremely scarce, like the Middle East. (Not all of these plants source water from the ocean—brackish water, or water with a higher salinity content than freshwater but lower than that of the sea, can be found in river estuaries that meet the ocean and can also go through the desalination process to produce potable water.) In the U.S., around 200 desalination plants are in operation today, with the majority located in California, Florida, and Texas.
Desalination on a modern, industrial scale looks a lot different from what those ancient sailors used. While some plants do still use thermal technologies—using heat to separate the salt and the water—in most modern industrial plants, seawater is filtered into a plant using membrane technologies, where water is sucked up from the ocean and then forced through a membrane with openings small enough to filter out the salt, a process called reverse osmosis. (The membrane does such a good job, in fact, that minerals need to be added back in to the resulting water because it’s so pure.)
The first issue with this process might sound obvious: a lot of stuff lives in the seawater getting pulled up to be desalinated. Older desalination systems used to harm larger marine life by forcefully pulling it up against intake systems; a technology called subsurface intake—the process of drawing up water through sand from below the ocean floor—has been one solution. But there are many organisms that live in the water, like baby fish, eggs, larvae, that can enter desalination plants with even the most up-to-date technology.
These animals “get sucked up into the system, and they all just die. It’s a small part of the food chain, but it is part of the food chain, and [desalination] just kills billions of larvae each year,” Bothwell said. “It’s a significant impact to the food chain along the coast.”
It’s not just what gets sucked into plants that poses a problem for the ocean. The potable water produced by desal plants has an evil cousin: the super-salty discharge that remains, a substance known as brine, which is roughly twice as salty as the original seawater. Brine is heavier than seawater and can sink to the bottom of the ocean, where it creates a deoxygenated dead zone. The world’s desalination plants are estimated to produce more than 37.5 billion gallons of brine each day (they produce more brine by volume than drinking water); the proposed Huntington Beach plant would have produced about 57 million gallons of brine each day. The plant’s proposal included a technique to forcefully release the brine into the ocean, mixing it with seawater and preventing it from sinking as a mass to the ocean floor—but, regulators found, that dispersal process was also harmful to ocean life and would kill organisms in about about 100 billion gallons of seawater per year.
Fortunately, reverse osmosis produces less brine than older thermal tech. More than half of the world’s brine, experts have estimated, is created by plants made in just four Middle Eastern countries that use older technologies. Some researchers are working on possible uses for the brine, including making it into chemicals to help with the desalination process itself. But there’s no question that excess brine from a growing desalination industry could become yet another stress on an already-stressed out ocean.
“Our ocean is already under a ton of different pressures: nutrient runoff, ocean acidification, climate change,” said Bothwell. “You add desal on top of it, and it creates a dead zone.”
Desalination isn’t the only strategy that involves sacrificing ecosystems in order to help humans survive global warming. Technology in the age of extreme climate change looks increasingly like a game of tradeoffs—figuring out how to responsibly manage renewable energy projects, for instance, that need to be sited in ecologically sensitive areas, or how to mine responsibly for all those minerals we’re going to need. As the world warms and water crises mount, there are real questions about how best to incorporate complex technologies like desalination.
“We can’t be in California and say no to all desal,” Bothwell said, noting that his organization supports some smaller desalination projects, where the environmental impacts are much smaller. Desalination plants that deal with less-salty water—inland plants that treat brackish water or water that’s otherwise too salty for consumption—also produce much less brine and are ecologically less harmful than ocean desalination.
The human tradeoffs of desalination, not just the ecological ones, are also important to consider. It takes a lot of energy to suck ocean water through that almost-impermeable membrane, meaning that desal plants, if they’re connected to a fossil-fueled grid, can add to climate change-charged droughts like the one in the U.S. West. Just around 1% of desalinated water made in the world is created by renewable energy, so there’s a lot of ground to cover to make sure that existing facilities get cleaner. All that energy can get pricy and impose costs on the people who use the least water.
“One of the reasons desalination is so expensive is that it’s energy-intensive—it’s one of the most energy-intensive water supply options that we have,” said Heather Cooley, director of research at the Pacific Institute. “In the places where we’ve seen people build it, we do see the rates go up. There are cheaper options that have fewer environmental impacts and impacts on communities.”
Raised rates may be more acceptable if a community has no other options. But counterintuitively, desalination projects aren’t always placed where there’s a need for water. Take the Huntington Beach plant, for instance. The latest water use analysis for Orange County, where Huntington Beach is located, found that the county has enough water to meet demands, even during dry years, through 2045. The costs of adding water using desalination to that system would have been big: A 2016 analysis from the Pacific Institute found that ocean desalination plants like the Huntington Beach project would produce water at a median cost of $2,100 per acre-foot, making it one of the most expensive methods of providing freshwater. (Desalination of brackish water, the Pacific Institute analysis found, is a lot less expensive.) That, in turn, would have made the cost of water for people in the region “moderately to severely less affordable,” a 2019 UCLA analysis of the proposal found.
Both Cooley and Bothwell point out that simpler and cheaper methods of providing freshwater have not yet been fully tapped. The same Pacific Institute analysis found that stormwater capture projects could provide water for around $590 per acre-foot. Recycled water projects, meanwhile, are more expensive than stormwater capture but significantly cheaper than ocean desalination.
“There are billions of gallons of water we discharge to the ocean annually that we could be recycling,” Bothwell said. “Why should a company like Poseidon be pushing a rock up the hill, when they could be pushing it down the hill and be doing more cycling?”
Communities could also do a lot more with efficiency measures and figure out ways to reduce the current amount of water they consume. “It’s not uncommon to see emerald green lawns that are irrigated poorly,” said Cooley. “If you look at our urban water use in California, half is for landscapes. There’s a lot of doom and gloom around drought and around climate change and water use, but we have significant opportunities to be doing better than how we’ve been doing.”
Even Newsom’s administration, which has previously voiced its support for desalination, has been more constrained of late. In a water supply strategy plan for the state released in August, desalination is a core component—but mostly through brackish desalination, the less expensive option, with orders for the state to identify and expedite brackish desalination projects that can be operational no later than 2040 and review groundwater basins to get a sense of how much is available for desalination. For ocean desalination, the plan proposes simply developing new criteria for siting plants along the coast.
Ocean desalination projects approved since Huntington Beach was denied illustrate some of the thorny issues at hand. In October, California regulators approved a desalination project at Dana Point in Orange County that would deliver water to around 35,000 residents. The project is much smaller than Poseidon’s proposed behemoth (producing 5 million gallons of water per day versus 50 million) and would mainly serve a population that currently pays high prices for water imported from other areas, whose supply lines are at risk from earthquakes or droughts. While briny discharge would still be an issue, the Dana Point project was lauded by some environmentalists for its intake design, which would use slanted wells under the ocean floor that should significantly reduce the risks posed to marine life.
But less than a month later, regulators approved another desalination project in Monterey County that drew much harsher criticism. While the plant is around the same size as the one in Dana Point and would use a similar intake design, this facility came under fire from environmental justice advocates, who pointed out that it could increase rates for water by up to $50 per month and is located in a residential area already burdened by industrial facilities.
“Desal doesn’t need to be this contentious, and the fact that this project is, points to a problem here,” California Deputy State Controller Kristina Kunkel said at a hearing about the project.
As the world gets drier, there’s no question that ocean desalination can fit into our water future. But tapping into the seemingly endless supply of the ocean is more complex than it looks at first blush. The promise of desalination is understandably alluring, but a focus on it while ignoring simpler solutions shows how some see climate change as a problem to be solved with technology, rather than finding ways to fix broken systems and to make do with less. Real, sustainable change comes from making the harder, systemic fixes first—not chasing after expensive technology.
“We need to do the cheaper things first,” Cooley said. “We don’t know what the future holds. And the things we’re talking about doing are consistent with a good quality of life—it’s just about using less water.”