Solar solution for dirty water

For cheap clean water, take an old plastic bottle and just add sunshine… Put unsafe water in a plastic bottle, shake it up, put it on a corrugated metal sheet in the sun for a few hours and… it’s drinkable. Sounds unlikely, but SODIS (solar water disinfection) is backed by the World Health Organisation as a cheap, simple way of providing clean water to the world’s poor. It works by using radiation and heat from the sun to kill pathogens in the water - and it provides a neat means of recycling used plastic bottles too. SODIS was devised by the Swiss Federal Institute for Environmental Science and Technology in 1991, and is now being used by around one million people in 20 countries. According to research by Dr Kevin McGuigan of the Royal College of Surgeons in Ireland, it’s highly effective against the pathogens responsible for such illnesses as cholera, typhoid, bacillary dysentery, gastroenteritis, polio and giardia. He added that field trials in Kenya had shown children who drank SODIS water were seven times less likely to get cholera than those who drank untreated water, while the incidence of serious diarrhoeal diseases in general was 20% lower. There are a couple of caveats: SODIS is only really effective with clear water, which should be filtered before treatment; similarly, it does not work as well if bottles are badly scratched. While it kills an estimated 99.99% of biological pathogens, it doesn’t remove chemical contamination. But at local level, its effects can be dramatic. Ryan Sinclair, who coordinated a SODIS pilot in Cambodia for the Adventist Development Relief Agency, said the incidence of diarrhoea fell by around 80% in the first month after launch. Ryan drank only SODIS water during the yearlong project. “At first I was a little bit nervous, but some expats were using filters and they were getting diarrhoea, and then when they started using SODIS they were all right.” - Alison Winward

20 September 2005

Alison Winward