Villages in Tanzania are using the sun’s rays to purify their drinking water, saving time and energy. Pastor Moses Kwanga is behind the project, which aims to educate rural populations on this easy way to purify their water supply.
The sun heats the water, helped by the black roof, which helps to absorb the heat. Solar radiation means a combination of ultra-violet rays and heat destroys the bacteria which cause common water-borne diseases like cholera, typhoid, dysentery and diarrhoea. After eight hours in the sun, it is ready to drink. If the water reaches more than 50C, it is safe in just one hour.
Link via BBC
You would think that if this were a reliable way to purify water, it would be more widespread. Why is Dean Kamen spending so much time and money on a powered water purification system? Granted, it runs off of cow dung, and generates 1000 liters of water per hour, but it will still cost a lot to manufacture each unit.