Providing clean water is an integral part to any effort to raise third-world living standards. Solvatten, a Swedish-designed water purifier, does its job using nothing but a couple of hours in the sun.
The Solvatten looks like a standard jerrycan sliced in half and divided into two 5 liter compartments, each of which has a clear face. The two chambers are exposed to sunlight, which naturally heats the water to a pathogen-killing temperature of roughly 130° F. An indicator changes from red to green when the water is safe to drink.
The whole process takes about 3 to 4 hours when its sunny, and 5 to 6 when it's cloudy. While that's not perhaps the fastest way to cure water, the amount of resources it saves compared to boiling over gas stoves makes it ideal for making sure some clean H2O will be on hand later. [Treehugger]