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Sustainable Way to Purify Water: Folded Saris Filter Out Pathogens

Posted By Prucia Buscell, Thursday, March 22, 2012
Photo by Rita Colwell

Women in small villages in Bangladesh are using an ingenious method to fight cholera - a waterborne disease endemic in many parts of the developing world where clean drinking water is unavailable. In areas where fuel to boil water is scarce and expensive, woman are using old saris, the bright colored garments nearly every woman wears, folded between five and eight times, to filter water before they use it.

Dr. Rita Colwell, Distinguished University Professor at both the University of Maryland and the Johns Hopkins University Bloomberg School of Public Health, had hypothesized that removing particulate matter from water could remove most of the bacteria that causes cholera, and lab experiments showed that a sari folded multiple times could remove 99 percent.

In a PopTech conference interview, Dr. Colwell described a three year study, funded by NIH, that showed a 50 percent reduction in cholera in a village where she and colleagues laid out an experimental design on filtration by sari. She and colleagues hired extension agents, similar to agricultural extension agents in the U.S. who educated women on the bacteria in the water and the reasons why filtration would help. The women learned quickly. A study five years later showed between 60 to 70 percent of the women were still filtering, and women in other villages had begun filtering as well because the women who learned the technique initially became teachers. Even those who didn’t filter benefited, because there was less cholera to spread in the local environment. The sari cloths used as filters are always available and easily cleaned by rinsing and drying in the sun.

"We think households can provide themselves with good water that significantly reduces many of the waterborne diseases in a way that’s sustainable and that doesn’t cost anything,” Dr. Colwell said. "It’s a matter of education and individual empowerment.”

Women in developing countries often get water for their families from nearby rivers that also serve as a communal toilet, bath and sink, creating an environment where disease causing pathogens flourish. According to the CDC, mortality rate for cholera is as high as 50 percent in countries that lack adequate medical facilities.

Dr. Colwell and colleagues have tracked climate change by satellite and correlated the data to cholera outbreaks. A Harvard School of Public Health story explains that the bacterium V. cholerae, which causes cholera, attaches itself to tiny waterborne animals called copepods. The copepods feed on phytoplankton, which bloom when water temperature rises. Dr. Colwell and colleagues also discovered that when water temperature drops, the bacteria survive in a dormant, non-culturable state. That explains why cholera bacteria suddenly emerge in waters previously thought to be free of the pathogen.

Dr. Colwell was awarded the 2010 Stockholm Water Prize, widely recognized as the world's premier award for water related research or policy work.

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