How scientists made a cheap new filter to purify water

Stanford University created a cheap, nanowire filter that kills nearly all the bacteria it comes into contact with. The new filter might fend off waterborne diseases in developing countries.

Standford University researchers developed a cheap water filter that could help purify water in the developing world — providing a new way to treat waterborne diseases like cholera, typhoid, and hepatitis.

The filter is cheap and kills off most bacteria it touches.

After purchasing the cotton fabric at Wal-Mart, the scientists wove it into a filter by immersing it in a solution of carbon nanotubes. After the scientists let the fabric dry, they dipped it into silver nanowire solution.

And voila, the scientists created a filter that can work 80,000 times faster than traditional filters.

In laboratory tests, the new type of filter killed 98% of the Escherichia coli bacteria. All it took was a few layers of the fabric filter and a charge of 20 volts of electricity.

The filter is fundamentally different than the filters on the market because it doesn't attack the bacteria physically. It actually lets the bacteria pass through, killing it as it slips through its electrical field.

"This really provides a new water treatment method to kill pathogens," Stanford engineering professor Yi Cui said in a statement. "It can easily be used in remote areas where people don't have access to chemical treatments such as chlorine."

How did Cui know it would work? He knew silver had a reputation as a bacteria killer.

Cui said before people had refrigeration and pasteurization, people would go as far as putting silver dollars in their milk and sometimes even put the money in their mouth. Gulp.

Thanks to gravity, the water pours right on through — so no pump is necessary!

The energy requirement is so low, Cui figures the filter could be powered by batteries, by riding a stationary bike, or by simply turning your hand.

Bye, bye bacteria?

Photo: Yi Cui, Stanford University

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