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These Moisture Harvesters Collect Drinking Water, Even In The Driest Climates

Even in the driest places on Earth, there's water—it's just a matter of figuring out how to get it. Though machines that harvest moisture from the air have been around for years (after all, Luke Skywalker's family would have never made a living without them) a new model is capable of conjuring enough drinking water for an entire family, even in the middle of the desert. Sci-fi, meet reality.

The water harvester, built at MIT, uses MOFs synthesized at Berkeley to suck water from dry air. The harvester uses sunlight to heat the MOF, driving off the water vapor and condensing it for use.

How to Squeeze Water from Dry Air

Fog harvesters have been in use for decades, but as you can probably guess from their name, they need a lot of water in the air in order for them to work. We're talking 100 percent humidity. And there are methods for getting water from drier air, such as dew harvesting, but that requires keeping the collector extremely cold, making it expensive and impractical. The new moisture harvester, developed and tested by an MIT team led by Evelyn Wang, is a passive system that doesn't carry such a huge energy cost and takes its energy from the sun.

The secret ingredient is a special material known as a metal-organic framework, or MOF. It's comprised of organic molecules bonded to metallic ions in an arrangement that forms a rigid structure riddled with tiny holes. It's inside these holes that the water accumulates. The system has proven itself capable of harvesting about a cup of water per kilogram of MOF over the course of just 70 minutes. That's in 20–30 percent humidity, which is about as low as it gets here on Earth. In other words, this is a life-saving contraption even in the planet's driest deserts.

A metal-organic framework, or MOF. The lines are organic linkers, and the red and black balls are metal ions. The yellow balls represent the holes that can be filled with gas or liquid. The background image shows individual MOF crystals, which are packed into the water harvester.

Water For The World

Many parts of the world have been experiencing moderate to severe droughts, and four billion people around the globe face extreme water scarcity for at least one month out of the year. So is it possible that this new moisture harvester could be the solution they have been searching for? Researchers have high hopes.

Professor Omar Yaghi, inventor of the MOF, is thrilled by the possibilities. "One vision for the future is to have water off-grid, where you have a device at home running on ambient solar for delivering water that satisfies the needs of a household." With MOF costing about $10 per kilogram, the material isn't just amazingly efficient, it's also cost-effective. It all adds up to the very real possibility of solving water shortage problems within a few short years.

The complete water harvester. The MOF is just below the glass plate on top, which lets in sunlight in to heat the material and drive off the absorbed water. The yellow and red device at the bottom is the condenser, which is covered with water droplets.

Can Air Be A Water Source During A Drought?

Written by Reuben Westmaas May 1, 2017

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