Sri Lanka and the Tsunami

The ultraviolet (UV) radiation from the Sun's rays eliminates virtually all disease-causing bacteria, viruses and micro-organisms.

In northern Brazil, residents in the town of Oroba are using an altogether different method in order to purify water and prevent disease.

The town's inhabitants have taken to a surprisingly simple process called Sodis (Solar Water Disinfection Process).

There are several stages to Sodis. Firstly, a clean, two-litre bottle needs to be filled up to three-quarters of its volume with water.

The bottle is shaken for 20 seconds to oxygenate the water. Then, the rest of the bottle is filled and the top screwed on.

It is then placed on a rooftop in direct sunlight for six hours. The ultraviolet (UV) radiation from the Sun's rays eliminates virtually all disease-causing bacteria, viruses and micro-organisms.

"This method is very efficient if you follow the simple procedures," says Professor Jose Euclides Paternini of the Unicamp University, Sao Paolo.

"The Sodis method can be used in many countries, but especially those close to the equator with high solar radiation, and where the population has no access to conventional water treatment."

Luiz Barbosa has been a community health worker for 10 years, looking after 118 families in Oroba. He has observed the difference Sodis has made to the health of his community.

"The water treatment we are using here in this municipality is Sodis - that is purification through the Sun's rays - and it is working well because the children are healthy, smiling and they're enjoying a healthier life," he explains.