The Sari-Cloth Water Filter

The solution to controlling cholera will be high-tech analyses to produce extremely low-tech solutions.

– Dr. Rita Colwell

Cholera is a pathogen which, in humans, causes uncontrollable diarrhea so severe it can lead to death. While almost unknown in the first world, it is still an intractable problem in the third world, where many people lack access to safe, clean drinking water.

In Bangladesh, the problem is particularly dire. Villagers often must drink from the same ponds and streams which become contaminated with sewage overflows during the monsoon season. This leads to cholera rates which a recent World Press Review article estimated at between a quarter and a half million cases each monsoon season. While some water filtration devices exist, they are often prohibitively expensive for general use in this, one of the world’s poorest countries.

Rita Colwell, the former head of the National Science Foundation, worked for three years on the problem of cholera in Bangladesh. Dr. Colwell noted that all water for village consumption was gathered by women, and so she focused her efforts on the women of Bangladesh.

When she spoke with village women in poor rural villages, she found that it was difficult for them to follow the standard recommendation to boil water for 20 minutes before drinking it. Fuel for fires is scarce in Bangladesh, and therefore far too precious to be used for something as mundane as simply boiling water in a prophylactic way.

Filtration was another option. Cholera bacteria can be filtered out of water relatively easily, because cholera bacteria survive in water by attaching themselves to larger plankton. When filters remove the plankton from contaminated water, most of the disease-causing bacteria are removed as well. However, the nylon filters in existence are expensive. In order to ensure that every woman who gathered water had access, a cheaper, more viable filtration solution was needed.

As Dr. Colwell explained in a 1999 interview, “The thought was, ‘What could be used as a filter that exists in everyday life?’ The answer was cloth, sari cloth, which even the poorest of the poor have.”

Colwell and her team conducted tests. They filtered water, and examined different samples with electron microscopy. After lab analysis, they found the magic formula; by pouring contaminated water through sari cloth folded 8 times, more than 99% of the cholera bacteria was filtered out. In test villages where all women were taught this method, the number of cholera cases dropped by more than 50%.

The older and more frayed sari cloth worked best.

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