Playpumps
Problem - it's hard for many developing countries to get clean water. They must daily walk back and forth to the source with jugs. But there is water right below them - they just need to tap into it.Solution - Playpumps harness the endless energy of kids. as they play on the merry-go-round, it pumps the water and stores it for use.
Brilliant.
Video.
link via how to change the world