Texas-based researchers have developed a sustainable plant-based material that could potentially reduce or eliminate reliance on bottled water while addressing water scarcity, a major global issue.  

The material, known as a hydrogel, acts like a sponge, pulling in moisture from the air and releasing it when heated at low temperatures. It can be used anywhere, even in remote, off-grid locations with low humidity levels, and the absorbed water is safe for drinking.

“The water collected from our hydrogel meets international safety standards, with metal ion concentrations well below the World Health Organization limits,” said Guihua Yu, the study’s lead investigator and a professor at The University of Texas at Austin’s Materials Institute.

Globally, at least two billion people lack access to safe drinking water, a number that is expected to climb as the climate continues to heat up. In response, the United Nations is aiming for “universal and equitable access to safe and affordable drinking water” by 2030.

As the atmosphere holds an estimated 13,000 trillion kilograms of water, tapping into this abundant resource could be the key to meeting this target.    

Sourcing water-harvesting materials from nature

Yu and his team at created the hydrogels by chemically modifying cellulose, starch, and chitosan –– a compound found in crustacean shells and fungi –– to enhance their ability to absorb and release water.

Polymeric hydrogels, while good at retaining water, are often made from petroleum-derived polymers, Yu said. Unlike fossil fuels, which have limited reserves, biomass materials are renewable, so their supply is ensured. 

The modification process involved grafting certain functional groups onto the chemical structures of cellulose, starch, and chitosan to improve water retention and promote water desorption at lower temperatures, making the process more energy-efficient.

The researchers also embedded lithium chloride, a salt, within the hydrogel to boost its water-absorbing performance. Due to their chemical structures, salts have a natural affinity for water, a property known as hygroscopicity—this is why salt is so effective at preserving food.   

“Unlike free salts, which can dissolve and leak, we immobilized lithium chloride within the hydrogel matrix, allowing it to retain its hygroscopic properties while preventing unwanted loss,” Yu explained.

“This combination ensures that the hydrogel remains highly effective in capturing atmospheric moisture, even in arid conditions,” he added.  

How practical are the hydrogels?

To find out how much water could actually be harvested from the hydrogel in a real-world scenario, the researchers tested the cellulose-based hydrogel, which had the highest water uptake in initial indoor tests, in an outdoor experiment in Austin, Texas.

For six days, they alternated between absorption and desorption cycles, in which the water captured by the hydrogel from the air during each absorption cycle was evaporated by heating the hydrogel on an electric hotplate at 60 °C. They collected the water vapor by condensing it onto a glass covering above the hotplate.

The researchers found that 95% of the captured water could be released at this temperature over each four-hour heating period. Based on the amount of water collected during each desorption cycle, they calculated that a kilogram of the sorbent can provide over 14 liters of water per day on average. 

According to Yu, this amount of water exceeds what other sorbents being investigated for atmospheric water harvesting, including metal–organic frameworks, have been reported to yield. These materials can also require much higher temperatures to release the stored water. 

Aside from the environmental benefits, including avoiding plastic waste and the carbon dioxide emissions associated with bottled water production and transportation, atmospheric water harvesting has the potential to be much more economical than buying bottled water.

Based on the current average price of bottled water in the United States and considering operational costs, Yu and his colleagues estimated that the hydrogel-based water harvester could fully offset its initial investment costs within a year of use.

“Over multiple years, the savings could amount to hundreds to thousands of dollars per household, depending on water needs and local bottled water prices,” Yu said.

Yu and his team are currently working on improving the energy efficiency and practicality of the hydrogel sorbent and its water-harvesting process.

“Moving forward, we aim to enhance the hydrogel’s performance by optimizing its porosity and internal water transport pathways to accelerate sorption–desorption kinetics,” Yu shared.  

Yu and his team are also developing hydrogels that can use direct sunlight, rather than electric heating, to drive water release, which would lower the energy consumption even more.    

“Scaling up production is another key focus, as we work toward making these materials viable for widespread deployment in water-scarce regions,” Yu stated.

Reference: Weixin Guan, et al. Molecularly Functionalized Biomass Hydrogels for Sustainable Atmospheric Water Harvesting. Advanced Materials (2025). DOI: 10.1002/adma.202420319

Feature image credit: Weixin Guan et al.