These devices harvest drinking water from the air in the planet’s driest places. Critics say they’re an expensive distraction

By Laura Paddison, CNN

(CNN) — The arid desert landscape of Death Valley is not the obvious place to find water. Yet it’s here, in one of the planet’s hottest and driest places, that Massachusetts Institute of Technology engineers decided to test new technology to pull drinking water from an unconventional source: the air.

Their water harvesting device is a window-sized panel made with absorbent material called “hydrogel,” which has been infused with salt, folded up like origami and enclosed in glass.

The material, which looks like black bubble wrap, absorbs water vapor directly from the air, swelling up as it does so, then shrinking again as the water evaporates. The water condenses on the glass and flows down a tube to emerge as fresh, drinkable water. No power is needed, just heat from the sun.

The device doesn’t produce a huge amount of water from the bone-dry air — around two-thirds of a cup a day — but the ultimate aim is to supply a household with drinking water even in arid deserts, said Xuanhe Zhao, a mechanical engineering professor at MIT.

Water scarcity is a huge global issue. More than 2 billion people lack access to safe drinking water, a situation set to worsen due to climate change, which fuels longer and more severe drought. As reservoirs shrink, groundwater dries up and rainy seasons become more erratic, some believe one answer to this crisis lies in the reservoirs of moisture in our skies.

Atmospheric water harvesting is a tantalizing prospect and a rush of new research is generating excitement, but there are sizeable obstacles: It has historically been energy intensive, it produces small amounts of water and even the new methods are many times more expensive than tap water.

Sucking water from thin air is not new. For centuries people have collected it from the fog rolling in from oceans or over mountains using vegetation, containers or mesh nets to catch water vapor and condense it.

More recent techniques use condensation to cool moist air and form liquid — the same principle that creates moisture on the side of your cold drinking glass on a hot day — but it requires high humidity.

Scientists like MIT’s Zhao have been developing technologies to work even in arid climates. This type of water harvesting relies on desiccant, the same stuff that’s in those little packs put into shoe boxes and new bags to suck up moisture and prevent water damage.

Some desiccants are solid, others are liquid but the newest — hydrogels or aerogels — are spongy.

“They can swell like 10 times their volume just by sucking humidity out of the air” and work even in very dry environments, said Paul Westerhoff, a professor at the School of Sustainable Engineering and the Built Environment at Arizona State University. It’s “where a lot of the excitement in the field is,” he told CNN.

Hydrogels tick a lot of boxes, said Evelyn Wang, a mechanical engineering professor at MIT. They are low cost — they’re the same material used in diapers — and don’t require much energy to release the water they absorb, she told CNN.

There’s been an explosion of research into hydrogels. One project used a hydrogel-salt mixture to pull drinking water from the air in the Atacama Desert in Chile, the driest non-polar place on Earth. The device made around 0.1 gallons per square meter per day, according to a study published last month.

Another project says it can create a gallon of drinking water a day from the air in Las Vegas using a hydrogel membrane “skin” inspired by tree frogs and air plants. “This whole idea seemed like science fiction, but this is possible, and we’re actually doing it,” H. Jeremy Cho, a mechanical engineering professor at the University of Nevada, Las Vegas, said in a statement.

Some experts, however, believe it will be extremely difficult to overcome atmospheric water harvesting’s biggest problems: cost and yields.

“The fact remains, you’re making quite a small amount of water and it’s also very difficult to think where it fits in the menu of water sources,” said Christopher Gasson, the owner of the research publication Global Water Intelligence. It’s “going to be a niche thing, if anything,” he told CNN.

Steve Gluck, an independent water industry consultant echoed this. “In most cases, it’s a lower tier solution,” he told CNN.

Almost everyone agrees it’s expensive. “It would cost about 10 times more than the tap water I buy from a city today if I were to drink it,” Westerhoff said. It’s also more expensive than desalination, the process of creating freshwater from seawater.

But it is cheaper than bottled water. This makes it “good for small-scale applications where you need a small amount of high-quality, potable water,” said David Warsinger, a mechanical engineering professor at Purdue University. He pointed to places where tap water is unreliable or untrustworthy, like Flint, Michigan, during its lead crisis, or parts of Bangladesh where water is contaminated by arsenic.

Drinking water, however, is not the best first use of atmospheric water harvesting, Westerhoff said, industry would be better.

The technique could provide “ultra pure water” needed to manufacture semiconductors, or the very clean, desalted water required for making products like batteries, soda, beer and medical equipment, he said.

Water harvesting could be used in emergency situations like hurricanes where people lose access to water and power. Soldiers could use the devices in the field, although Gasson remains skeptical even of that. “Think about the volume of kit that you would need in order to supply military with the water it needs in the middle of nowhere,” he said.

There are broader concerns, too, about atmospheric water harvesting and whether it might increase global drying trends. But it’s not like mining, Westerhoff said, because the water is being borrowed and put back into the global water system in a small window of time.

Westerhoff predicts an “explosion” in some commercial uses as the technology scales up and gets cheaper, although he still believes it will be at least a decade before it really takes off.

There is already a lot of activity.

Israeli company H2OLL, which runs air through a liquid salt solution, has been running a commercial pilot system in a Bedouin school in the Negev Desert that can produce more than 200 gallons a day, said Joab Kirsch, the company’s CEO. It believes its tech will be most useful for dry inland regions, including in the southwestern United States, Mexico and India.

Delaware-based AirJoule aims to use industrial waste heat to produce around 800 gallons a day of “pure distilled” water, said Bryan Barton, the company’s chief commercialization officer.

The global market is valued at more than $2 billion. “To the critics, you show them the money is growing in atmospheric water harvesting, so they are missing something,” Gluck said.

Gasson, however, thinks it’s a distraction. Atmospheric water harvesting is booming in popularity because “people love the idea of it being the silver bullet,” he said.

“We shouldn’t be getting wound up about trying to take more stuff out of nature. We should be thinking about how we can do more with the water that we’ve already taken from nature.”

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