High Marks for Clean Water

June 14, 2010 1:45 pm

Water is disinfected using the sun’s energy in the Kibera slum of Nairobi, Kenya. Photo: Sven Torfinn, Panos

Retrieve a discarded water bottle. Tear off the label and fill with any water that’s not too murky from a creek, standpipe, or puddle. Place the bottle on a piece of metal in full sun. In six hours the UVA radiation will kill viruses, bacteria, and parasites in the water, making it safe to drink. SODIS, the acronym for this Swiss-pioneered water-disinfection program, is now being used all over the world to provide drinking water for some four million people. “It’s simple, it’s free, and it’s effective,” says Ibelatha Mhelela, principal of the Ndolela Primary School in Tanzania. In 2006 her school started using SODIS to disinfect its contaminated tap water, placing bottles on the building’s corrugated metal roof. The result? Absenteeism due to diarrhea dropped considerably, and examination scores soared. “Before we started SODIS, only 10 to 15 percent of the children passed the national sixth-grade exams,” says Mhelela. “Now 90 to 95 percent of the students pass.” —Mark Jenkins

ALL BOTTLED UP Continuous, strong sunlight does all the hard work of SODIS. But the following tips help the process along.

1. Use bottles of clear PET plastic rather than glass. Studies show water from sun-warmed PET is safe to drink.
2. Do not disturb bottles while they sit in the sun.
3. Store water in bottle to prevent recontamination.

National Geographic Magazine,  April 2010

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