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.