Researchers from MIT and Stanford have come together to ask whether reliable drinking water can be made from the air we breathe. And, if it can, what has been stopping us from doing it?
Water is in a vulnerable situation right now. According to Schneider Electric’s sector president for water and environment, Sophie Borgne, by 2030, the gap between the demand for fresh water and available supply is expected to reach 40%, meaning we are running critically short. Add to this that approximately half a million US citizens do not have access to clean, running water, and an estimated quarter of the global population lacks safe access altogether, and a picture of the growing urgency to conserve water becomes clearer. Then, of course, AI and data centres are only compounding the water problem by being greedy H20 guzzlers as they consume vast amounts of water in their cooling systems.
Moisture mission
There is a huge amount of water on Earth. More than 70% of the planet’s surface is covered in it, from oceans and ice caps to rivers, lakes, and soil. The atmosphere holds a smaller but still significant portion of this. Atmospheric water is everywhere, above every desert, city, and remote village on the planet. Scientists have calculated that Earth’s atmosphere contains around 13,000 trillion litres of fresh water at any given time. The challenge is capturing some of that water reliably, safely, and cheaply enough to matter.
To tackle this, the researchers investigated materials called hydrogels, which are very absorbent, jelly-like solids that are loaded with salt. Salt is really adept at pulling moisture from the air, and the hydrogel acts like a sponge that holds onto that moisture without it leaking out. The idea is that the material absorbs moisture from the air overnight, and then gentle heat is applied during the day to release that captured water as clean, drinkable liquid. This simple and non-invasive idea means that it is potentially usable anywhere in the world.
The only problem is that the materials kept falling apart. And if they don’t last, neither does their fresh water potential.
The problem with copper
In real water-harvesting devices, the gel sits on a metal surface – usually copper – which acts as a heater to release the captured water. When the team placed their hydrogel onto copper, it disintegrated in under three weeks. There was something about the copper that was destroying it.
What they found was that the copper was slowly releasing tiny amounts of itself into the surrounding liquid in the form of dissolved copper ions. Those ions then reacted with oxygen and water to produce highly reactive chemical molecules, which the researchers describe as behaving like wrecking balls, ripping apart the gel’s internal structure from the inside out. The gel went from a firm, functional solid to a useless liquid. Not only this, but the degradation compromises the safety of the water for drinking.
The team found that this problem was specific to copper. When they tested other metals commonly used in harvesting devices, such as iron, iron oxides, and aluminium oxide, the gels remained intact. This is because those metals are far less likely to release ions into the surrounding liquid under the conditions used in these devices.
What’s new?
The solution, as it turned out, was very simple. The team painted the copper surface with a commercial anti-corrosion varnish before placing the gel on top. This created a protective barrier that stopped the copper from releasing ions in the first place, and with no ions, there were no wrecking-ball molecules, and no damage to the gel.
With this fix in place, the hydrogel survived more than 190 absorption and release cycles across 96 consecutive days, and it kept working. In that time, the material captured and released the equivalent of almost 500 kilograms of water per square metre of gel. Previous experiments had only managed to demonstrate stable performance for fewer than 30 cycles.
The cost difference
Without durable materials, harvesting water from the air costs roughly the same as bottled water – anywhere between $0.10 and $1.00 per litre, which makes it an impractical solution for communities that need it most. With long-lasting materials, such as the hydrogel and varnished copper combo, the researchers calculate that the cost could fall below $0.01 per litre, which starts to bring it on par with what households in cities like Boston or Charleston, West Virginia, currently pay for tap water.
Could there be consequences?
Water in the atmosphere is part of a continuous natural cycle. It evaporates from oceans and land, travels through the air, and falls back as rain or snow. If vast quantities were extracted before that process completed, it could, in theory, leave less moisture available in certain regions, meaning less cloud cover, less rainfall, and drier conditions over time. That said, the atmosphere is enormous, and the volumes the research teams are looking at are comparatively small, as they envision this technology being most useful in localised, community-scale applications rather than as a global extraction operation. Which is sensible because though the balance of the water cycle is resilient, like all things in nature, it is not infinite.
If successful, this could be a great idea that goes a long way to help solve the world’s water crisis. However, with the vast amounts of water that data centres will need, will we just be swapping one crisis for another?
