Using the sun to sterilize water

Villagers in Tanzania seal plastic water bottles and leave them under the sun. Within a couple of hours, the water is clean enough for drinking purposes! If the sun is hot and the water reaches up to 50C, then it is fit for drinking within an hour. The technique still faces some hurdles due to cultural quirks, but it is an excellent way to purify stagnant or standing water, and should be publized in other parts of the world.