Water From Thin Air? (fastcompany.com)

How to Conjure Water From Thin Air

BY Cliff KuangTue Jun 2, 2009 at 2:02 PM
Researchers at the Fraunhofer Institute in Stuttgart say they've invented a novel way to turn air moisture into drinking water, thus helping solve the dire water shortages that face much of the world.

Here's how it works. First "hygroscopic brine"--a saline solution which absorbs moisture--runs down a tower, soaking water from the air as it moves along. It's then sucked into a vacuum-sealed tank. There, solar collectors heat up the brine. Thanks to the vacuum, the solution's boiling point is relatively low--so it's easy to create steam that then condenses into drinkable water. Presto! The remaining solution then runs down the tower, and the process repeats itself. The entire assembly is powered by the aforementioned solar collectors and solar panels, so that all of its energy needs are self contained.

The scientists have already tested the basic concept in the lab, and they're now trying to assemble a test facility. They think it could be particularly useful in places like Israel's Negev desert, where, even despite the parched conditions, the air's humidity is 64%--meaning that every cubic meter of air contains 11.5 millileters of water. But there are obvious challenges ahead. We're thinking the real secret sauce is how to keep the hygroscopic brine itself from evaporating as it runs down the tower--and that the biggest challenge will be running a facility like this which needs much less water added to it than it ultimately produces. Moreover, how do you force enough air across the surface of the tower, to produce a sizable enough water harvest? That problem of getting enough air exposure has bedeviled open-air carbon-capture systems--though water is admittedly an order of magnitude more plentiful in air than carbon dioxide.

Solving all those problems would be the equivalent of creating a perpetual motion machine for water generation.