Story Publication logo July 14, 2008

UV Rays to the Rescue


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In Ethiopia and Kenya, dry seasons grow longer and tribal conflict over access to water is on the...

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ON A FRAYED MAT ON ONE of the dusty streets of Kibera — Africa's largest slums — in Nairobi, Sophia Mohamed sells her wares: two mangoes, five oranges, a half-dozen calcium-based chewing stones and a pan brimming with bhajia (a potato snack).

Most of the goods, save for the bhajia, are arranged on a rusty metal rack beside her. It is here that Sophia spends her days, eking out a living. On a good day she makes Ksh50 (75 US cents). She is the sole bread winner of a family of eight. Her family's health also relies on four water bottles lying on the roof of her makeshift stall. The water is undergoing purification using the sun's rays through a technique known as solar water disinfection process (Sodis).

It is an open secret that tap water in the slum is contaminated with sewage. The water, which Ms. Mohamed usually buys from vendors or community-based organisations in the slum, gets infected in the pipes on its way to the reservoirs. In Kibera, sewage and water pipes run side by side through the only open spaces available in the crowded slums. Here water pipes, sewage and garbage also compete for space with the few pit latrines available. By late afternoon when Sophia is ready to retreat to her shack, the water in the four bottles too, after hours under the sun, is safe for drinking. This water purification process involves simply exposing the liquid to the sun's ultraviolet (UV) rays. In just hours, the UV radiation from the sun's rays will have killed the micro-organisms in the water.

BEFORE ADOPTING the simple household water purification technology, Sophia and her family suffered from various water-borne ailments. "My children and grandchildren used to vomit and suffer from frequent bouts of diarrhea," she said. "I was always at the hospital because I never used to boil the drinking water." But that was more than three years ago. According to Joshua Otieno, programme officer in charge of Sodis at the Kenya Water For Health Organisation (Kwaho), one only needs to put contaminated water in a transparent plastic bottle and expose it to the sun's rays for six hours or more.

The UV rays kill all micro-organisms in the water. On a cloudy day, the water should be left outside for longer, said Otieno. Started in Kibera by Kwaho in 2004 after a successful pilot project in 2001, the use of Sodis has spread among the slum dwellers.

It is a straightforward water treatment process which, according to Otieno, involves three simple steps: cleaning the bottle, filling the bottle with water and exposing the bottled water to the sun for six or more hours. Kwaho has recruited promoters who sell new two-litre water bottles at a subsidised price of Ksh10 to the slum residents. The organisation also collects empty water bottles from local eateries and big hotels in the city, which they then pass on to the people in the slums to use in the water-prurification process. Otieno, however, cautions that the technique only works during bright sunny days.

If there is more than 50 per cent cloud cover, the water should be exposed to the sun's rays for at least two days. The drawbacks are that Sodis cannot be used during rainy days and only a small amount of water at a time — below three litres — can be purified this way, he says.

At the Stara Primary School and Rescue Centre, a few metres from Mohamed's shack, pupils pick their purified bottled water from the ironsheet rack in the middle of the school compound and replace them with new ones filled with untreated water to be picked tomorrow. The pupils use two sets of bottles to maintain an adequate supply of safe drinking water to the school of more than 550 children says teacher Mary Muthini. Muthini — who heads the Sodis programme in the school — founded the school in 1999 as a feeding programme for orphans and extremely poor kids in Kibera.

Since adopting Sodis, Muthini says cases of waterborne diseases among the pupils are fewer. So far, it is estimated that 65,000 households in the Kibera and Mukuru slums in Nairobi have adopted the simple technology, says Otieno. Mother of one Habiba Ismail, 25, has more than 15 bottles she uses for the water purification. On any given day, she says she puts between five and seven bottles on her roof, to expose the water to the sun's rays.

She said the technology is not only simple but affordable compared with boiling. Despite the success of the project in Kibera, there are those who have refused to adopt the method on grounds that they are using other methods to purify their drinking water. However, most of these people it has been noted, are not using any water-treatment methods. Otieno says that the Sodis water-treatment method is used worldwide by millions of people. According to the sodis website (, communities in more than 20 developing countries around the world have adopted the technology. The World Health Organisation (WHO) has also been promoting the technique in sunny and hot countries, according to the BBC website (

According to the Sodis website, in 1991 the Swiss Federal Institute for Environmental Science and Technology) and its Department of Water and Sanitation in Developing Countries, conducted extensive laboratory and field tests to develop and test the Sodis process. The research over the years proved that the simple method of exposing small quantities of water to the sun's rays was efficient to kill disease-causing micro-organisms in water.

This international research accorded credence to local research conducted with water samples from Kibera. Celine Obuya, a senior laboratory technologist with the Ministry of Water and Irrigation at the Central Water-testing lab says that Sodis is an effective method of purifying water.

OBUYA AND HER TEAM collected water samples from various points in Kibera. The first was at the main Nairobi City Council water line before it enters Kibera; from pipelines and taps inside Kibera and from water reservoirs in Kibera. They also got samples of contaminated water collected from the slum and purified using Sodis. The results showed clean water at the main city pipeline before Kibera, but the water from the pipeline, taps and reservoirs inside Kibera was contaminated.

The results also showed clean, pure water after application of Sodis. The tests also showed that most of the water from pipes and water reservoirs in Kibera was contaminated with bacteria, especially E.coli. But after Sodis, the water tested negative for E.coli and other bacteria in each of the five tests that she has conducted. Obuya, however, warns that Sodis cannot be used to purify water that has suspended solid waste. The failure for the sun to disinfect such water, she says, is because suspended particles hide the micro-organisms and the sun's rays will not penetrate well to kill the organisms. She advises that the solid waste should be filtered first before exposing the water to the sun's rays. Sodis cannot be used to purify water polluted by chemicals. In the four years since Kwaho introduced the Sodis technique, impact studies show that cases of diarrhea recorded in medical clinics in Kibera have been reduced by 41 per cent says Otieno.

Following the success in Kibera and other slums in Nairobi, Kwaho is planning to take the technology to Migori, Wajir, Kisumu and Mombasa. The organisation has held training workshops in Tanzania, Uganda, Ethiopia, Zimbabwe, Benin and even in Latin America. In 2005, Kwaho won the Energy Global Award for its use of Sodis. Plans are underway to start a Sodis reference centre for East and Central Africa.



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