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SODIS - A place in the sun

Clean water is one of the world’s scarcest resources, with over a billion people lacking access to safe drinking water according to the World Health Organisation (WHO). Could it finally be time to shine for solar disinfection?

Solar water disinfection, also nicknamed SODIS, is a cheap, reliable method of killing the germs in untreated water, with no fancy gadgets or gizmos required. ‘Basically, what people do is they get an ordinary plastic bottle with a lid, fill it with whatever water they have available, and then they place that in direct sunlight for a minimum of six hours,’ explains Dr Kevin McGuigan, senior lecturer at at the Royal College of Surgeons in Ireland and a leading proponent of solar disinfection.

A ray of hope

The result? All harmful bacteria and almost all other pathogens, including viruses and parasites, are eradicated. This procedure can thus prevent diseases such as cholera, dysentery, typhoid and other waterborne diarrhoeal diseases, which cause an estimated 5000 deaths each day in developing countries. ‘We’ve yet to find a waterborne disease that’s not significantly affected by solar disinfection,’ enthuses McGuigan. Further studies have also dispelled the myth that leaving plastic bottles in the sun releases carcinogenic chemicals into the water.

SODIS works thanks to the combined harmful effects of ultraviolet (UV) radiation and heat on micro-organisms in the water. UVA  radiation passes through the bottle, damaging pathogens’ DNA and cell wells, and also creating hydroxyl radicals – ‘they are like little organic chainsaws that cut up long chain molecules,’ says McGuigan. ‘In addition, as the water heats up, the repair mechanisms in the cells become less and less efficient.’

Despite its benefits McGuigan stresses that SODIS is a temporary solution: ‘You can’t rely on the sunshine every day. Everybody would still be aspiring to have a chlorinated water pump. But from an infrastructure point of view, it’s very difficult to have a safe and reliable water distribution system out in Masai Land (Kenya) or in the middle of the Mekong Delta.’

Other methods, such as treating the water with chlorinated tablets or boiling it, are simply too costly for many people in the developing world. SODIS is also an effective emergency solution in case of natural disasters which can disrupt water supplies.

Although McGuigan and his research consortium are working on ways to enhance the efficiency of the process, the biggest hurdle for solar disinfection to overcome is not a technical one.

Too good to be true?

Even with solid research backing the idea, it has been sluggish to catch on. McGuigan encountered skepticism in the aftermath of the 2004 tsunami, when distributing clean water was a big problem. ‘We approached various NGOs and aid agencies and asked ‘have you considered solar disinfection?’ and the response we got was ‘I’ve never heard of it’ or ‘how do you think sticking water in a plastic bottle is going to do anything?’ That’s when we realised that there was a big disconnect between the established science and the dissemination of the know how.’

Oddly enough, SODIS’s startling simplicity is perhaps one of the main barriers to its uptake. ‘It’s such a simple procedure that people very often don’t trust it,’ elaborates McGuigan. ‘So we’ve spent the last 17 years doing the lab work, doing the field work and proving that it works. The challenge now is selling the idea to people who don’t necessarily see how an old plastic bottle could be the solution to a lot of their problems.’

McGuigan and his team received a €1.9 million EU grant in 2006 to continue spreading the word, kickstarting projects in Kenya, Zimbabwe, South Africa and Cambodia. Slowly but surely, progress is being made, with several NGOs recognising the benefits of SODIS, including the WHO, the Red Cross and UNICEF. ‘It’s now in use every day in 33 countries by about 2.5 million people,’ says McGuigan.



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7 October 2009

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