IF YOU LIVE in a desert, maintaining a supply of fresh water is a challenge. One answer is desalination, but that needs a source of brine from which to remove the salt—which in turn requires that your desert be near the sea. Even in inland deserts, though, moisture is often present in the air as water vapour. The problem is extracting this vapour effectively and cheaply. And that is what two groups of researchers—one at the University of Connecticut, the other at the University of California, Berkeley—hope they have managed to do.
The ease with which water can be won from air depends on that air’s relative humidity. This is a measure of its current vapour content as a percentage of its maximum possible vapour content at its current temperature. A relative humidity of 100% means the air in question is holding as much water vapour as it possibly can. A good way to get air to give up some of its moisture is therefore to cool it to the point where its relative humidity exceeds 100%.
Sometimes this happens naturally at night, causing mist and dew to form. These can be collected in special traps in areas where liquid water is otherwise rare. But if nocturnal cooling does not bring air all the way up to 100% relative humidity, building water traps out of special materials might give nature a helping hand.