Every fifth-grader hooked on adventure stories devours tales of shipwrecked sailors drinking seawater, with fatal results. The nerdy adult version of that adventure might be Saudi Arabia’s fantasies of towing (salt-free) icebergs from Antarctica back in the 1970s. And, of course, if you’re a Californian worried more about flooding this year than drought next year, harvesting fresh water from the sea sounds like an idea picked up from the Jetsons.

But in an era of rapid climate change, not to mention quasi-religious faith in the redemptive powers of technology, the idea of tapping the sea to fill the reservoirs (and swimming pools) of coastal megacities doesn’t seem so farfetched. Meanwhile, as seven Southwestern states squabble over rights to Colorado River water, the idea of large-scale desalination is getting a serious hearing. Here’s a brief on where we stand on desal, and why the experts are so deeply divided over its potential.

Desal 101

Population growth and increasing dependence on irrigation for high-value crops almost guarantees rising demand for water with a very low salt content. More to the point, the natural distribution of fresh water is highly uneven and growing ever more unpredictable. Exhibit A: the shrinking Colorado River basin and the predicament of the 40 million people who have grown highly dependent on it. Hence the renewed interest in tapping the one source of water that is effectively inexhaustible: the oceans.

Desalinated water is produced by either distillation or by a membrane filtration process known as reverse osmosis. Both yield potable water, but both require expensive, unsightly infrastructure and a great deal of energy to operate — with most of it currently coming from burning fossil fuels. And both typically involve returning super-salty brine to a vulnerable environment.

A Voice from the Past, and the Future

In 1961, President John F. Kennedy commemorated the opening of one of the first seawater desalination plants in the United States in Freeport, Texas. “No water resources program is of greater long-range importance than our efforts to convert water from the world’s greatest and cheapest natural resources — our oceans — into water fit for our homes and industry,” he argued. “Such a breakthrough would end bitter struggles between neighbors, states and nations.”

World peace remains elusive, but there are now about 21,000 desalination plants in operation around the globe. Forget the icebergs: the world’s largest desal system is located in Saudi Arabia (Ras Al-Khair Power and Desalination Plant) with a capacity of over 300 million gallons per day. The largest in the Western Hemisphere is the Claude “Bud” Lewis Carlsbad Desalination Plant, north of San Diego, which produces 50 million gallons per day. The San Diego County Water Authority agreed to purchase the entire output of the plant built and operated by the Poseidon Water Company for 30 years — which explains why Poseidon was willing to invest $1 billion upfront.

Aside from size, there is another big difference between these two plants. The Saudi plant uses thermal technology, which as the name implies, involves boiling seawater and collecting the condensed vapor to produce distilled water. Saudi Arabia, with very little fresh water and lots of cheap oil, produces more desalinated water than any other nation — a fifth of the world’s total.

The Carlsbad plant uses reverse osmosis technology, which pushes saline water through a semi-permeable membrane at tremendous pressure to produce a combination of drinkable water and concentrated brine. It works well, but at a cost. San Diego County’s primary fuel to make the electricity that operates the pumps is natural gas — and lots of it.

Indeed, according to a recent analysis by environmental economist Michael Hanemann of Arizona State University, the cost of desalinated water from Carlsbad is about $2,725 an acre-foot (the amount needed to cover an acre one foot deep), compared with an already-expensive $1,295 to $1,769 that the San Diego County Water Authority pays for water sourced from the Colorado River and the Sacramento San Joaquin River Delta.

“That is really expensive water,” said Jay Lund, a professor at the University of California at Davis. “The only reason I can think for San Diego doing that is to diversify their water supply. If the San Diego and Los Angeles water districts got along better [they compete for water delivered by the giant Metropolitan Water District] they probably wouldn’t have done it.”

Battle Lines Drawn

Poseidon Water’s website offers a brighter version of the story. Poseidon notes that the Carlsbad Plant, which opened in 2009, is the only water source in San Diego County that is not dependent on snowpack and rainfall — not a small thing in light of natural (and unnatural) weather changes. As part of the deal, Poseidon also enhanced public access and recreation in the marine environment through the dedication of more than 15 acres of lagoon and oceanfront land for public purposes in Carlsbad and restored 66 acres of wetlands in South San Diego Bay. More striking yet, the energy-intensive facility has been made carbon- neutral in the sense that it offsets its indirect emissions from burning all that gas with payments to reduce emissions elsewhere.

Poseidon does acknowledge that the plant produces a gallon of concentrated brine for every gallon of potable water – the salt has to go somewhere. But it points out that the brine “is diluted before it enters the ocean in accordance with environmental regulations and as approved by the Regional Water Quality Control Board.”

Not everybody buys Poseidon’s pitch. “Poseidon takes in 300 million gallons a day, treats 100 million in reverse osmosis, then gets 50 million gallons of potable water, and takes the other 50 million with 100 percent of the salt and mixes that with the 200 million [of regular-strength seawater] they diverted, and dumps it back into the ocean,” explains Robert Glennon, a law professor emeritus at the University of Arizona. “Per the environmental community: you couldn’t imagine a worse way to contaminate estuaries and habitat.”

A coalition of environmental groups, Native American tribes and climate change activists fought the Carlsbad plant to no avail, though they had more luck in blocking Poseidon from building a twin in Huntington Beach, about 60 miles up the coast from Carlsbad. “Poseidon would have killed more than 5 billion small ocean animals, overcharged ratepayers by more than $1 billion and failed to provide increased water supplies where they are needed,” argued Susan Jordan, executive director of the California Coastal Protection Network.

But last October the California Coastal Commission did point the way toward compromise. It greenlit a much smaller $140 million desalination plant in Dana Point, a few miles south of Huntington Beach, that will yield a modest 5 million gallons of fresh water daily. That plant includes technology seen as less malign by environmentalists. And unlike Huntington Beach, the Dana Point location has unique hydrogeology that will allow slant wells to draw water from beneath the ocean floor, thereby protecting marine life.

There currently are 12 desalination plants operating in California. Just where desalination is going in California is still anyone’s guess, and probably depends on changes in the sense of urgency created by the threat of drought. “California needs to diversify our water portfolio and stretch existing supplies as extreme weather threatens to reduce the state’s water supply,” Governor Gavin Newsom said in a statement in November 2022 — notably, before the big rains drenched the state in the coming winter.

The Incredible Shrinking River

You could write a book about the tragedy of the Colorado River, and quite a few people have. A common theme emerges: boosterism led river planners and myopic politicians to make unsustainable commitments.

Indeed, over a century ago, scientists were already warning that the river could not support the farms and cities that developers wanted to build.

In 1922, states in the river basin negotiated the Colorado River Compact that apportioned the water, with the so-called upper basin states (Colorado, New Mexico, Utah and Wyoming) getting 7.5 million acre-feet a year and the lower basin states (Arizona, California and Nevada) getting 8.5 million. A treaty later guaranteed Mexico, where the river reaches the sea, 1.5 million acre-feet. But the idea that the river’s flow would average 17.5 million acre-feet per year was never realistic.

The river’s actual flow has averaged less than 15 million acre-feet annually, and in each of the past three years the flow was less than 10 million. That hasn’t stopped agricultural and residential development, though, which have caused demand to soar over the past two decades even as supply stagnated. Lake Powell and Lake Mead, the showpiece reservoirs that store the river water and drive electricity turbines as it flows south, are shadows of their once-mighty selves.

After several deadlines on usage cuts came and went, the Biden administration proposed to put aside first-come-first-served precedent and minimize the economic and environmental damage by evenly cutting state water allotments — an approach that would reduce the water delivered to California, Arizona and Nevada by as much as one-quarter. The three states did sign an agreement to share cuts. But it only runs through 2026. And a return to profligacy-as-usual could mean true disaster for the lakes in the short run and massive economic dislocation for the Southwest in the long run.

What does all this have to do with desalination? Thrown for a loop by this entirely predictable crisis, states dependent on the Colorado River have been taking a fresh look at a desal fix. But, alas, there’s not much there: seawater sources are too far away, the obstacles en route too daunting.

“I don’t see much potential,” said Lund of UC Davis. “You’re looking at a need for three to four million acre-feet per year, with most of that for agriculture. Some of that [agriculture] is pretty valuable, but maybe not valuable enough for desalination; most of it is growing stuff to feed cattle.”

Actually there is already a 70 million gallon- a-day desalination plant on the Colorado River built a half-century ago to collect brackish irrigation water that finds its way back into the river and clean it up in order to meet obligations to deliver fresh water to Mexico. But the costs were out of sight and the plant has been out of service for some time. The auguries for another try on a much larger scale are hardly promising. “Even if you found a way to make it viable, it wouldn’t be enough to cover the deficit from overuse, over-allocation and global warming,” Lund opined.

The Accidental Sea

In 1905, an engineer — think sorcerer’s apprentice — tried to divert some of the Colorado’s flow into a canal running west into southern California. The canal was breached, and the entire volume of the Colorado River poured into what was then the Salton Sink, a geological depression more than 200 feet below sea level. The water continued flowing for nearly two years, creating what became known as the Salton Sea.

Engineers eventually stopped the flow. But drainage from river-irrigated cropland in California’s Imperial Valley replenished what was lost to evaporation, stabilizing the Salton Sea’s volume. As farmers cut back their runoff amid the drought, though, the Salton Sea has shrunk, and the rate at which it concentrates dissolved mineral salts has accelerated. It is now a witches’ brew twice as saline as seawater, which makes it too salty for all but the most adaptable life forms. And as water recedes exposing the seabed, winds are blowing toxic dust to nearby desert communities. The locals are thus pushing the idea of importing ocean water and purifying it in order to move back the clock.

But a review by a panel of experts concluded that the approach wasn’t feasible. “We deliberated for more than a year,” said Glennon of the University of Arizona, who served on the panel. “There were 18 proposals. … Most involved desalinating water from the Pacific or the Sea of Cortez [aka the Gulf of California]. The Pacific ones were most intriguing because it was the shortest distance, but it had the most challenging technical things you had to do — including going over mountains.”

The proposal that got the most traction involved building a large desalination plant at tiny Puerto Penasco on the Gulf of California, sending freshwater flowing 190 miles north through two pipelines. The concept also called for building a desal plant at the Salton Sea to reduce the salt content of the water already trapped there.

The proposed plant would be 20 times the size of the Poseidon facility at Carlsbad and would require a lot of electricity to operate. Since desal plants must run 24/7, wind and solar wouldn’t suffice without massive energy storage capacity. “The consulting team emerged outraged,” said Glennon. “Why would we foul up a pristine environment to try to rehab an artificial failed environment? What are you going to do with 20 times Poseidon brine?” Oh, and then there’s the small matter of cost, estimated between $66 billion and $78 billion …

The Elephant in the Water

Brine is the dirty secret of seawater desalination. In the process of making fresh water, desal plants have to produce concentrated brine that is typically returned to the sea. This produces a super-salty environment and raises water temperature at the disposal site, which many ocean creatures cannot tolerate. The brine often also contains concentrations of chemicals added in the desalination process, including copper and chloride compounds. “If you look at the database of all the desalination plants, they don’t talk about the brine,” noted Manzoor Qadir, a professor at the United Nations University Institute for Water, Environment and Health, in Canada.

There are ways to produce desalinated water more benignly, but they add to costs, and the new technologies that minimize the environmental impact have yet to work at large scale, Qadir added. “I am told the industry is doing their best, but that’s an area that needs more attention.”

Small Is Beautiful?

Since reverse osmosis is used to produce most of the world’s desalinated water outside the fossil-fuel rich Middle East, improving that process seems the right approach if desal is to become more than an asterisk in regional water supplies. Researchers at Purdue University have demonstrated something they call “double-acting batch reverse osmosis,” which they say promises better energy efficiency, longer-lasting equipment and the ability to process water of much higher salinity.

“About a third of the lifetime cost of a desalination plant is energy,” explained David Warsinger, an engineer at Purdue. “Even small improvements to the process — a few percentage points — could save hundreds of millions of dollars and help to keep CO₂ out of the atmosphere.”

Not to be left behind, MIT researchers have developed a decentralized approach to desal, a portable unit weighing less than 10 kilos. The suitcase-sized device, which requires less power to operate than a mobile phone charger, can also be driven by a small, portable solar panel and still generates drinking water that exceeds World Health Organization quality standards.

Unlike other portable desal units, the MIT device utilizes novel electrical techniques to remove impurities, eliminating the need for high pressure pumps and membrane replacements. The prototype generates drinking water at a rate of 0.3 liters per hour, a veritable drop in the ocean. But the researchers are working on scaling it up.

An Abu Dhabi-based startup called Manhat has developed a floating device that it claims distills water without electricity. It’s reminiscent of the solar stills that grade school students built as science projects. (Do they still do that?) Manhat employs a greenhouse- like structure that floats on the ocean surface. Sunlight evaporates seawater in the greenhouse, and as temperatures cool in the night, the water condenses into freshwater.

But will it scale? The prototype covers 2.25 square meters and produces just 1.5 liters of fresh water per day. (People in affluent western countries typically use 200-400 liters to drink, cook and clean.) Manhat says it is working to increase this volume to five liters by optimizing materials and design, with the long-term goal of reaching at least 20 liters. “We have to accept the fact that seawater should be a key player in providing freshwater,” Saeed Alhassan Alkhazraji, the company’s founder and associate professor at Abu Dhabi’s Khalifa University, told CNN. “But we need to have a solution that will minimize CO₂ emissions and eliminate brine altogether.”

Back to the Future

Lund, for one, doubts that any of these processes will have a large impact. “Technology may help, possibly a bit, not a lot,” he concludes. “There’s a fundamental thermodynamics to separating salt molecules from water molecules. You can find the cases for desal, but I don’t see it being more than one or two percent of water supply in places like California.”

The more one looks at desal, the more convincing the case for getting ahead of water shortages by focusing first on the boring lowtech stuff like roofing irrigation canals to reduce evaporation and capturing billions of gallons of water from storm runoff. Then there’s the stuff that makes us squirm: with each drought, treatment of secondary sewage water becomes a more palatable idea.

But it may not even be necessary. “Farmers consume 80 percent of U.S. water,” reminds Robert Glennon. “If we can just get that down to 75 percent, the municipal water problem is solved — and we can do that, with a robust plan to modernize farm water irrigation systems. Half of all farms in the Colorado basin flood irrigate; it’s a very wasteful system. They could be more efficient, use less water for the same amount of product, and the cities would get the water they need.”