Clean water at no cost, the SODIS way

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SIMPLE AND SAFE: A resident lays out water bottles to be treated by solar energy and heat. PHOTO: Shivaji Rao
SIMPLE AND SAFE: A resident lays out water bottles to be treated by solar energy and heat. PHOTO: Shivaji Rao

Kannal Achuthan

WHO-approved technique catches on

Chennai: Residents of some low-income settlements in the city have adopted a simple technique to obtain clean drinking water. All they need is a PET bottle and a few hours of the sun's energy everyday.

Solar Water Disinfection (SODIS), a technology approved by the World Health Organisation for low-cost water treatment in sunny countries, is being employed to destroy pathogens such as coliform bacteria.

In Chennai, this no-cost technology is being propagated in slums and low-income localities by LEAD, a non-governmental organisation. S. Spurgeon, communications officer at LEAD, says, "SODIS kills pathogens, which are the cause for many water-borne diseases. Our tests show that the treated water is free of bacterial colonies."

The SODIS method is quite simple. A PET bottle is cleaned thoroughly, filled with drinking water and laid on its side under sunlight. After six hours of exposure, the water can be cooled and consumed. Transparent bottles with `PET' written on the bottom can be used for SODIS. Only bottles of one or two litres capacity should be used which allow the sun's rays to penetrate easily. "Contaminated water gets treated in two ways: UV radiation and increased water temperature kills microorganisms," explains Marc Autenrieth, a scientist with Eawag, a Swiss federal agency that promotes SODIS internationally. Mr. Autenrieth, who was in Chennai recently, found that the pilot project taken up in some Chennai slums had become quite popular with the residents. One has to only walk into the Jothi Nagar slum tenement near Saidapet bridge to see how the idea has caught on. PET bottles full of water are laid out before houses and on terraces. Every household keeps at least five bottles under the sun for treatment everyday.


S. Nalini, a resident, said that she had been sceptical of the idea initially. However, after two months she was convinced. "Earlier, my family suffered from diarrhoeal attacks but now our health is much better. My son, an electrician, carries this treated water to work," she says.

Another resident M. Vasantha said that SODIS helped cut down on health bills as wells as expenses on kerosene used to boil water earlier. LEAD has introduced SODIS in slums in Saidapet, Besant Nagar and Korukkupet.

Many people were worried if using PET bottles could cause harmful effects.

However, scientific tests by Eawag have found that the treated water is safe for consumption. For more information, log on to or contact LEAD at 43519339.




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