Rural Bangladeshi women often pour sweetened drinks through a piece of sari cloth to get rid of leaves, insects and other visible debris. But disease-causing micro-organisms are thousands of times smaller than the pores in the fabric and slip right through.

About 10 years ago, a team of researchers in Maryland and Bangladesh came up with a ridiculously simple solution: Wash and fold the sari. Four thicknesses of laundered sari fabric, with its loosened, roughened cotton fibers, will strain out most of the microscopic plankton in water. In water contaminated by cholera, enough bacilli are attached to plankton for the quantity of cholera in filtered water to drop by more than 99 percent.