SUNLIGHT and oxygen are all that is needed to make dirty water clean enough to drink, according to the latest microbiology research.
The discovery, by Rob Reed, a senior microbiologist at the University of Northumbria in Newcastle, has major implications for developing countries where water-carried diseases are endemic.
His simple technique involves half filling a plastic or glass bottle with contaminated water and leaving it for a day in the sun, shaking the contents from time to time.
By the following day, the sunlight will have killed off 99.9 per cent of the bacteria, making the water drinkable.
The anti-bacterial properties of sunlight have been known for centuries and came to the fore in the 1980s when pioneering studies were carried out at the University of Beirut. But results so far have been variable.
Sometimes the technique seemed to work while at other times the bacteria remained active, making it too risky to introduce in practice.
Now Dr Reed has demonstrated that the effectiveness of solar decontamination depends upon the amount of oxygen present in the water.
This means that aerating the water before and during its exposure to sunlight, kills off the bacteria every time.
Dr Reed hit upon the idea while sitting on a beach in Greece and developed it in the less sunny climate of Newcastle.
It works as long as there is enough sunlight to create a shadow and relies on the light rather than heat effects of the sun so the bottled water never becomes too hot.
Trials of the process are to take place in Mozambique over the next few months.
"I can take 1 per cent of raw sewage here and inactivate the faecal indicators so that to all intents and purposes it would pass the requirements of drinking water," said Dr Reed.
"There is no reason to imagine that the organisms that cause dysentery and salmonella in other countries would not also be killed."
He said most water-borne diseases depended on their victims consuming a certain dose of bacteria. Even if the sunlight process failed to kill all the organisms, it would destroy enough to eliminate the danger of disease.
His discovery could transform life in countries with prevalent water-borne diseases.
The procedure needs no expensive chemicals or equipment and can be carried out by individuals, families or small communities.
It could be used in rural villages, urban shanty towns or mountainous locations, which may have access only to sewage-contaminated surface water.
Alternatively, it could provide emergency water supplies in war zones or to refugees.
Using the sunlight system is also easier than boiling the water using fuel wood, which is labour intensive and can lead to deforestation.