In many parts of the developing world, drinking a glass of water can be deadly — especially for young children, who can die of diarrheal diseases contracted from dirty water.
So getting clean water to people in the developing world has been a top priority for aid groups for a long time. But it's been a surprisingly hard problem to solve.
For a while, aid workers largely treated clean water as an engineering problem: If there's no clean water in a village, dig a well.