Forget expensive chlorination - Tanzanian villagers used free sunlight to sterilize their water.
"I fill the plastic bottles, put the lids on, then put them on my black-painted roof where they stay for a whole day."
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 diahorrea.
After eight hours in the sun, it is ready to drink.