Contrary to popular belief, purified drinking water from home faucets contains millions to hundreds of millions of widely differing bacteria per gallon, and scientists have discovered a plausible way to manipulate those populations of mostly beneficial microbes to potentially benefit consumers.

Their study appears in ACS' journal Environmental Science & Technology.

Lutgarde Raskin and colleagues Ameet Pinto and Chuanwu Xi explain that municipal water treatment plants typically try to minimize the growth of microbes in the huge filters that remove small particles and substances that can serve as nutrients for bacterial growth. These facilities also add chlorine or other disinfectants to kill bacteria and prevent them from thriving in water distribution pipes. Nevertheless, it's not possible to totally eliminate bacteria with current technology, making it important to determine how the filter and other water treatment steps impact the types and amounts of bacteria that remain. That's why the researchers set out to do this in a study at a treatment plant in Ann Arbor, Mich.

Their research provides suggestions on how to change which bacteria wind up in the drinking water. The scientists found that certain types of bacteria attach to the filters where they form biofilms from which small clumps can break off and make it into the drinking water supply. The water's pH was a strong factor in determining which bacteria made it into the drinking water. Measures as simple as varying the water pH or changing how the filters are cleaned, for example, could help water treatment plant workers shift the balance toward bacteria that are beneficial for humans by not allowing the harmful bacteria to compete.

The authors acknowledge funding from the National Science Foundation and the University of Michigan.