Safe drinking water from solar-powered Hydrogel

 Create free clean drinking water from solar-powered Hydrogel  

Researchers from Stanford University and MIT have developed a longer-lasting hydrogel that can pull moisture from the air and turn it into drinkable water using sunlight. During testing, the hydrogel, made with a moisture-absorbing salt and a polymer commonly found in diapers, produced up to two liters of drinking water a day. Researchers at Stanford and MIT improved the hydrogel which captures moisture from air and releases it as drinkable water using only sunlight. Adding an anti-corrosion coating significantly increased the material’s durability, allowing it to last more than eight months and over 190 harvesting cycles without contaminating the water. While still in early stages, the system could eventually produce water for about one cent/liter and provide a low-cost option in extremely dry environments. One in four people on Earth lacks reliable access to safe drinking water, according to the WHO. With this option, people may have a solution, even for those living in the most bone-dry desert on the planet. The work could help people in dry regions where traditional water sources are limited. WHO and UNICEF reported in 2025 that 2.1 billion people, still lacked access to safely managed drinking water.

Hydrogels are soft, sponge-like materials made from water-absorbing polymers which can hold large amounts of liquid. They're already used in everyday products like diapers, contact lenses, wound dressings and some beauty products. In this case, researchers combined a hydrogel with lithium chloride, a highly absorbent salt which pulls moisture from the air, even in extremely dry climates. When heated by sunlight, the material releases that moisture as water vapor, which can then be condensed into drinkable water. The material is a sponge-like mix of lithium chloride and polyacrylamide. Lithium chloride is a highly absorbent salt, while polyacrylamide is a polymer. Earlier field testing in Chile’s Atacama Desert used a panel of the material mounted on a black-painted aluminum sheet. The sheet absorbed heat from the sun and helped the hydrogel release collected water. Carlos Diaz-Marin, assistant professor of energy science and engineering at Stanford’s Doerr School of Sustainability and co-lead author of the study, said the improvement could eventually bring the cost of water produced this way to about one cent/liter. This would be about 1% of the cost of bottled water and close to the cost of tap water in some US cities, Stanford reported.

The research team published their findings in Nature Communications after testing a material called a hydrogel, a sponge-like combination of salt and polymer that scientists have been working to perfect for years to extract moisture from thin air. The sponge can then release the collected droplets as drinkable water using nothing but sunlight. The team explained that the product had been tested in the past but had fallen apart too quickly to be practical. "To our knowledge, nobody had thought of durability and degradation of these materials, despite it being a critical parameter for water production," Carlos Diaz-Marin, said. The current design can produce up to two liters of water/day using a thin layer of material spread across a panel roughly the size of a bath towel. Stanford said that is around the amount generally needed per person per day for basic health during emergencies. Diaz-Marin wants to increase the output. This could make the system more useful for rural communities in dry inland regions where desalination is not practical.

The hydrogel, the team explained, is made from two familiar ingredients: lithium chloride, a superabsorbent salt and polyacrylamide. In earlier field testing in Chile's Atacama Desert, which ranks among the driest places on Earth, a team of researchers deployed a "cookie-sheet-sized" panel (their descriptor, not ours, though rather appropriate for Food & Wine) of the material. During the day, the black-painted aluminum sheet absorbed heat from the sun, warming the hydrogel and causing it to release water as vapor, which was then condensed into drinkable liquid. However, the material only survived about 30 of those fill-and-release cycles before breaking down, which was nowhere near enough to make it economically viable or safe. This created both cost and safety concerns because degraded salt or polymer could enter the condenser and affect water quality. After four years of lab work, the team found that the metal surface holding the hydrogel was causing the problem. The metal released ions that formed damaging radicals inside the gel, which then broke down the polymer chains. The researchers fixed the issue by adding a commercial anti-corrosion coating to the metal. The coating blocked the ions from reaching the hydrogel. With the coating in place, the hydrogel stayed stable for more than eight months in stress testing and lasted for more than 190 water harvesting cycles. "Any degradation could make either the salt or the polymer go into the condenser," Diaz-Marin said. "That would basically destroy the potability of the water."

The paper said the coating strategy allowed stable moisture absorption and release for more than 190 cycles over 96 days. It also said the approach could create a path toward producing water from air for less than $0.01/liter. The technology is not ready for large-scale deployment yet, but the researchers are working to improve efficiency and reduce cost. The metal casing, which they noted is necessary for conducting the sun's heat, was releasing ions that generated damaging radicals inside the gel, which then chewed through the polymer chains. "The radicals are very efficient at eating the polymer away," Diaz-Marin said. The good news is that the fix is straightforward. All they needed to do was coat the metal with a commercial anti-corrosion coating to block those ions from ever reaching the gel. "These new hydrogels are exceptionally exciting because they give us a way to produce potable drinking water in really extreme conditions," co-lead author Chad Wilson, who worked on the hydrogel as a graduate student at MIT, added. The hydrogel approach is one of several emerging technologies designed to pull water from the air. Other researchers are also studying metal-organic frameworks, which can capture water at very low humidity levels. The new work shows that durability may be just as important as water capture itself. Without a longer-lasting material, water harvesting from air would remain too expensive and unreliable for practical use.

Diaz-Marin said that "We see a path to this technology to perhaps even being competitive with tap water,". The current design produces up to two liters of water/day, enough to meet a person's basic needs in an emergency. But Diaz-Marin wants five liters, to ensure that even those living in rural communities in arid regions where desalination isn't an option can have all the water they need. "There are a lot of people who don't have access to water or have to walk hundreds of hours per year to procure water," Diaz-Marin said. "We believe this could potentially be a way to provide additional water resources." While the technology isn't ready for large-scale deployment yet, Diaz-Marin said they are working on it quickly.  This isn't the only technology emerging that can pull water from the air. In April, F&W also reported on metal-organic frameworks, which can trap water at relative humidity levels as low as 10%, which is technically lower than the average humidity in Death Valley, California. Metal-organic frameworks are still in the early stages, too, but with the world entering a state of global water bankruptcy, these scientific findings can't come soon enough to help the effected areas.