By Gretchen Cuda Kroen (NPR) Pouring water into clear plastic bottles and placing them in the sun can kill disease causing organisms in about six hours. It’s a simple and cheap method that’s been around forever, and it helps. (Who says sun tea isn’t safe?)
But there’s a hitch – the water has to be clear enough for the sun’s rays to penetrate – and much of the world’s water supply is murky from the clay soils in riverbeds and lake bottoms that mix with the water. Enter the scientists.
“Basically, you need to be able to read a newspaper through it. That means it’s clear enough for the UV radiation to penetrate and kill the pathogens. If you can’t see through it, it just won’t work,” explains Joshua Pierce, associate professor of materials science and engineering at Michigan Tech.
Pierce and his colleagues discovered that by adding a little table salt to this murky water, they could get the particles of clay to stick together and settle to the bottom, making the water clear enough to purify using the solar disinfection method. They also found that the addition of salt works best for certain kinds of clay soils, namely bentonite, and not so well with others. But when they added a little bentonite along with salt to water that contained other types of clay soils, it worked just as well.