Science Daily recently published an article that discusses "mining" the air for water. Here's a summary of the process, which was invented by Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB:
"... hygroscopic brine – saline solution which absorbs moisture – runs down a tower-shaped unit and absorbs water from the air. It is then sucked into a tank a few meters off the ground in which a vacuum prevails. Energy from solar collectors heats up the brine, which is diluted by the water it has absorbed"
This sounds too expensive and equipment-intensive to be useful for people in developing countries. But who knows? (Photo courtesy of Fraunhofer-Gesellschaft.)
(Thanks to Greg Laden for suggesting this story.)