Pulling water from thin air in the Atacama

A low-cost device draws moisture from air in the driest place on Earth, the Atacama Desert in Chile (Device 2025, DOI: 10.1016/j.device.2025.100798). The device uses a water-absorbing hydrogel–salt material in a carefully designed architecture and produces 0.6 L of water per m ² per day at a relative humidity ranging from 15% to 38% between day and night in the desert.

On a rooftop in Cambridge, Massachusetts, the device harvested 1.7 L/m²/day at 50% relative humidity. It’s a “unique, practical solution for decentralized water production” in arid regions, says Georgia Institute of Technology mechanical engineer Bachir El Fil, who led the work.

Atmospheric water harvesters use advanced materials such as hydrogel-salt hybrids and metal-organic frameworks (MOFs) to absorb moisture from cool night air and then release the water as the harvesters warm up in the sun. Hydrogels can hold much more water than MOFs, but they pull it from the air slowly, which makes them inefficient in low humidity.

El Fil and his colleagues designed a hydrogel-based system that collects water 10 times faster than MOF-based devices. They made a hydrogel with cross-linked polyacrylamide polymers and loaded the material with lithium chloride. At 30% relative humidity, 1 g of the hydrogel-salt composite holds 2 g of water, more than MOFs can hold.

The researchers optimized the thickness of the hydrogel and the size of the air gap between the material and the condenser plate that collects the water vapor. These adjustments speed the flow of water through the hydrogel and the flow of water vapor across the air gap.

Most water-harvesting research focuses on improving the sorbent material itself, says Guihua Yu, a mechanical engineer at the University of Texas at Austin. The Georgia Tech researchers’ system-level optimization leverages the hydrogel’s moisture-absorbing properties “to achieve higher real-world water productivity and efficiency than previous systems,” Yu says.

Deployed in the Atacama in the summer of 2024, the device produced water at a relative humidity as low as 11%, El Fil says. And its best performance was more than 2 L/day in 30% humidity, which is “among the highest reported under such dry conditions,” he says.

One concern with hydrogel-salt hybrids is the loss of salt as the material cycles between absorbing and releasing water, says Omar Yaghi, a chemist at the University of California, Berkeley, who is developing a MOF-based water-harvesting system. But this is a “very nice study that helps build understanding of how different materials work” for atmospheric water harvesting.