As much as bullets or body armor, rations or radios, an army needs water to survive — especially when it’s fighting in the blistering heat of an Iraqi summer. But hauling a soldier’s daily requirement of three to four gallons of water has become a gargantuan burden to U.S. armed forces. So Darpa, the Pentagon’s mad science division, has come up with a plan for thirsty GIs: Cut the amount of the water they’re carrying in half, and pluck the rest from out of thin air.

Even in the parched Mesopotamian desert, the air holds plenty of water. The trick is getting it out. Machines have been around for years that can cool the air down to the point where water droplets will condense like dew beading on an oak leaf. But they’re energy hogs, using almost 650 watt-hours just to get a single quart of H20. The goal of Darpa’s Water Harvesting program is to extract that water without using up so much power.

That would make a huge difference to troops stationed in the Middle East. “With the temperatures in August soaring well above 125 degrees (Fahrenheit),” writes Chief Warrant Officer Gordon Cimoli, a Black Hawk helicopter pilot who served 10 months in Iraq, “water is life.”

“If Darpa can pull it off it would be a tremendous weight off our back, both literally and figuratively,” a U.S. Army captain currently stationed in Iraq added in an e-mail. Water takes up to 40 percent of the Army’s daily logistical load, according to one military report — nearly 55 pounds of water per soldier per day, when medical treatment, meal rehydration and bathing are factored in.

The folks at Sciperio — a Darpa-funded research firm based in Stillwater, Oklahoma — think they’ve found a way to effectively wring water from the skies. When air passes over liquid lithium chloride, water vapor becomes trapped, instantly, explains Sciperio managing partner William Warren. The result is a brackish fluid, undrinkable by even the toughest soldier. Fresh water can be extracted, however, using a filtration process known as reverse osmosis. To oversimplify, the setup uses high pressure to drive the undrinkable liquid through a semipermeable membrane, which traps the salt and allows H20 to flow through. Usually, the process has to be repeated several times in order to get something potable. That wastes energy. But advanced pumps from Spectra Watermachines use the salty leftovers to re-pressurize the system, letting it act more efficiently.

Darpa has given Sciperio and its research partners about $4 million, so far, for the project. But while the individual components have been tested, the system as a whole won’t be ready until January or February, Warren said.

By then, three prototype Humvees could be in Iraq, supplying troops with water from an even less likely source than desert air: the fuel the vehicles run on. Diesel fuel is made of about 13 percent hydrogen. So when diesel exhaust is combined with oxygen and cooled down, water is the result, notes Marit Mazzeti, a manager at LexCarb, which has received about $2.5 million from the Army and Darpa for its water-extraction research.

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