The world needs more fresh water. Why isn’t desalination the answer?

There is obvious demand for the technology that makes seawater drinkable. And solar power should be making it more feasible. If only it were that simple.

By Saima May Sidik

Photo Illustration by Luis G. Rendon/Globe Staff; Adobe

The future will be hot and dry, and we will want more water. Even if global temperatures only rise by 1.5°C degrees Celsius above preindustrial levels by 2050, the UN’s Intergovernmental Panel on Climate Change estimates, 178 million people could live in places where intense droughts are common.

Whenever a severe drought comes around, people point out the irony of wishing for water on a planet that’s 71 percent covered with the stuff. And that brings up the idea of expanding desalination, the technology for removing salt from seawater or salty groundwater.

Some Middle Eastern countries have invested heavily in the technology and now get about half their potable water from desalination. That put them in the news when Iran reportedly bombed neighboring countries’ plants in the early stages of the war and President Trump threatened to do the same in Iran. In the United States, only about 1 percent of drinkable water comes from desalination plants, but the approach seems to be gaining traction. There’s no official national tally, but it’s thought that the country has over 400 plants with the collective capacity to crank out over 3 billion gallons of water per day.

One big problem with desalination has always been that it’s hugely energy intensive, which leads to high costs and high carbon emissions. But as the efficacy of solar energy has shot up over the last decade, solar-powered desalination has been touted as the future of our water supply. It’s been said that seawater desalination could alleviate projected water scarcity in 50 percent of coastal cities, and tapping into salty groundwater or transporting treated seawater inland could stretch the benefits even farther. Combined with renewable energy, desalination could be “transformative,” energy and water researchers wrote in a review article published last year. It’s a “game changer” that could “secure the future,” a group of proponents of the technology have written.

But others who study desalination roll their eyes at claims that it is poised to come down significantly in cost. “You can’t go by a day without seeing somebody saying how they’re going to reduce the cost of desal by 60 percent,” says Tom Pankratz, an independent consultant who has been working in the field since the 1980s. And when these substantial cost reductions do pan out, they’re usually in small-scale systems, not the type that’s needed to keep a megacity hydrated.

“There’s a particular tendency for people to come along with the next big idea in desalination technology because the allure is so great. If we could just get the technology right, then we could solve the world’s water problems,” says Joe Williams, a professor of human geography at the University of Bristol. But in reality, “it always turns out to be more complex than that.”

At this point, it’s possible that solar-powered desalination will keep millions of people hydrated in a hotter future — but it could just become another source of overpriced bottled water.

A desalination plant in Rishon LeZion, Israel, in 2014. Dan Balilty/Associated Press

Just out of reach

Solar desalination comes in a few different forms. Thermal stills use heat from the sun to evaporate water, leaving salt behind. The steam is then funneled into a separate chamber where it cools and turns into purified liquid water. Parabolic mirrors that track the sun and concentrate its rays have sometimes been used to accelerate this process. But the most widely used form of the technology is to force water through a membrane that removes salts. That can be powered by clean solar energy.

But you can’t just put a bank of solar panels next to a large-scale plant, because they would take up far too much space. In a study published in 2022, researchers predicted that by 2050, powering Israel’s desalination plants with solar panels would require 37 square kilometers of land — the equivalent of two-thirds of the city of Tel Aviv. And seawater desalination plants have to be located along the coast, where land is in high demand for tourism, recreation, and other uses.

The solution, therefore, is to run the desalination plant with electricity from the same power grid the rest of the region uses and put an equivalent amount of solar power into the grid elsewhere. On paper, the plants are solar-powered, but in reality they’re dependent on the same mix of power sources that everything else is using.

Whether adding solar to the grid lowers the cost of electricity — for a desalination plant or any user — is hard to say. It depends on the availability of solar in the region and the varying costs of fossil fuels. Last year, researchers from Lawrence Berkeley National Laboratory found evidence that solar has reduced electricity prices slightly, but by their own characterization, the evidence is weak.

There is reason to expect prices will edge down further. The cost of batteries is dropping rapidly, which could tip the scales in favor of solar power that is stored for use around the clock. But the cost of electricity is only about half the reason that the price of desalination is so high, Williams says. The high cost of building and maintaining the plant accounts for the other half. Gregory Pierce, who runs the Human Right to Water Solutions Lab at UCLA, has seen the cost of building a desalination plant run 30 to 50 percent higher than alternatives like recycling wastewater or capturing stormwater. Communities tend to build desalination plants because “they’re desperate,” he says.

Where solar could really increase the reach of desalination is in rural areas where the electrical grid is spotty and the locals only need a modest amount of clean water. In Kenya, for example, Western groups are building plants to provide clean drinking water to low-income villages. The plants provide an alternative to kiosks run by water companies, whose prices are set in agreements with the national water regulator. But even the cheapest desalinated water tends to cost four to five times what the kiosks are supposed to charge. The result is that desalinated water is out of reach for the poorest families who need it most. Elsewhere in Kenya, condo developers are building plants just to service their posh estates. It’s “almost designer water,” Williams says.

Reverse osmosis tubes inside a desalination plant in Carlsbad, Calif. Sandy Huffaker/NYT

In Mexico, gated communities in the beach town of Puerto Peñasco are served by desalination plants, but the average person doesn’t have the means to pay for this water, says geographer Anne-Lise Boyer from the University of Arizona. She’s seen small-scale solar desalination approached better in the Navajo Nation, where researchers worked with the community to figure out whether removing salt from groundwater would be a cost-effective way of meeting residents’ water needs.

In Kenya, there’s a simpler path to water security, says James Wambua Kaluli, an environmental engineer at Jomo Kenyatta University of Agriculture & Technology. Rainwater is plentiful in many parts of the country, but to capture and store it requires a 10,000 liter tank per household, which costs around $500 US. That’s out of reach for many Kenyans, but the tank can be refilled indefinitely, whereas the same amount of money would only buy about five tanks worth of desalinated water. “I wish more money would be invested in the storage of water,” Kaluli says.

So desalinated water doesn’t seem like it’s going to come cheap. And yet climate change is coming for us all. Even a critic of desalination like Williams has to admit that the technology might have a place in our future, given that projections for water availability are, in his words, “alarming.”

Desalinated water is expensive. But the cost of not having it may be even higher.

Saima May Sidik is a science writer based in Somerville.

This article originally appeared on BostonGlobe.com on July 19, 2026.