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Currently, 2.2 billion individuals around the globe are deprived of reliable access to clean drinking water. In the United States, over 46 million people face water scarcity, living either without running water or with water that is not safe for consumption. The growing demand for potable water is straining conventional resources such as rivers, lakes, and reservoirs.
To enhance accessibility to safe and reasonably priced drinking water, MIT engineers are utilizing an unconventional resource: the atmosphere. The Earth’s air comprises millions of billions of gallons of water in the form of vapor. If this vapor can be effectively captured and converted, it could provide clean drinking water in areas where traditional water supplies are unavailable.
With this objective, the MIT team has designed and tested a new atmospheric water extractor, demonstrating its ability to efficiently seize water vapor and generate safe drinking water across various levels of relative humidity, including arid desert air.
The innovative device is a black, window-sized vertical panel crafted from a water-absorbing hydrogel substance, enclosed within a glass chamber coated with a cooling layer. The hydrogel resembles black bubble wrap, featuring small dome-shaped formations that swell as the hydrogel absorbs water vapor. When the seized vapor evaporates, the domes shrink back in an origami-like transformation. The evaporated vapor then condenses on the glass, from where it can flow down and exit through a tube as clean, drinkable water.
This system operates entirely autonomously, without a power source, unlike other models that depend on batteries, solar panels, or grid electricity. The team operated the device for more than a week in Death Valley, California — the driest area in North America. Even under very low-humidity conditions, the system extracted drinking water from the air at rates up to 160 milliliters (approximately two-thirds of a cup) per day.
The researchers estimate that several vertical panels, arranged in a compact array, could passively supply a household with drinking water, even in dry desert settings. Additionally, the water output from the system should increase with humidity, providing drinking water in temperate and tropical regions.
“We have created a meter-scale apparatus that we hope to deploy in resource-constrained areas, where even a solar cell is not readily available,” states Xuanhe Zhao, the Uncas and Helen Whitaker Professor of Mechanical Engineering and Civil and Environmental Engineering at MIT. “This is an evaluation of the practicality in scaling up this water harvesting technology. Now individuals can construct it on a larger scale or design it into parallel panels to furnish drinking water to communities and achieve genuine impact.”
Zhao and his colleagues reveal the specifics of the new water harvesting design in a publication released today in the journal Nature Water. The lead author of the study is former MIT postdoc “Will” Chang Liu, who is now an assistant professor at the National University of Singapore (NUS). The MIT co-authors include Xiao-Yun Yan, Shucong Li, and Bolei Deng, together with collaborators from various other institutions.
Carrying capacity
Hydrogels are soft, porous substances primarily composed of water and a microscopic web of interconnecting polymer fibers. Zhao’s team at MIT has mostly investigated the application of hydrogels in biomedical fields, including adhesive coatings for medical implants, soft and flexible electrodes, and non-invasive imaging stickers.
“Through our research with soft materials, we have a strong understanding of how hydrogel excels at absorbing moisture from the air,” Zhao explains.
Researchers are investigating several methods to extract water vapor for drinking purposes. Among the most effective so far are devices constructed from metal-organic frameworks, or MOFs — highly porous materials that have also demonstrated the ability to capture water from dry desert air. However, the MOFs do not swell or expand when absorbing liquid, which limits their vapor retention capability.
Water from air
The team’s new hydrogel-based water harvester resolves another significant issue faced by similar designs. Other researchers have crafted water extractors from micro- or nano-porous hydrogels. However, the water yielded from these systems can be salty, necessitating additional filtration. Salt is an inherently absorbent substance, and researchers infuse salts — typically lithium chloride — into hydrogel to enhance the material’s moisture absorption. The drawback is that this salt can leach out with the water when it is eventually retrieved.
The new design from the team substantially minimizes salt leakage. They incorporated an additional component within the hydrogel: glycerol, a liquid compound that naturally stabilizes salt, keeping it contained within the gel rather than allowing it to crystallize and leach out with the water. The hydrogel’s microstructure lacks nanoscale pores, which further prevents salt from escaping the material. The salt concentrations in the water they gathered were below the standard limit for safe drinking water and considerably lower than those produced by many other hydrogel-based systems.
In addition to refining the hydrogel’s formulation, the researchers enhanced its shape. Rather than maintaining the gel as a flat layer, they shaped it into a pattern of small domes resembling bubble wrap, which increases surface area and the amount of water vapor it can capture.
The researchers manufactured a half-square-meter of hydrogel and encased it in a glass chamber resembling a window. They coated the exterior of the chamber with a specialized polymer film that helps cool the glass and prompts any water vapor within the hydrogel to evaporate and condense on the glass. They installed a simple tubing mechanism to collect the water as it cascades down the glass.
In November 2023, the team visited Death Valley, California, and arranged the device as a vertical panel. Over seven days, they recorded measurements as the hydrogel absorbed water vapor during the night (the time when vapor levels in the desert peak). During the day, aided by sunlight, the harvested water evaporated out from the hydrogel and condensed on the glass surface.
Throughout this period, the device functioned across a variety of humidity levels, from 21 to 88 percent, and produced between 57 and 161.5 milliliters of drinking water daily. Even under the most arid conditions, the device extracted more water than other passive and some actively powered models.
“This is merely a proof-of-concept design, and there are numerous areas we can optimize,” Liu remarks. “For example, we could develop a multipanel configuration. Additionally, we are working on next-generation materials to further enhance their inherent properties.”
“We envision a future where an array of these panels could be deployed, occupying a minimal footprint as they remain vertical,” Zhao adds, indicating plans to further test the panels in various resource-limited regions. “Then many panels could work in synergy, continuously collecting water at a household level.”
This research was supported, in part, by the MIT J-WAFS Water and Food Seed Grant, the MIT-Chinese University of Hong Kong collaborative research initiative, and the UM6P-MIT collaborative research program.
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