How does ultraviolet light kill microbes in drinking water?
-J. Welsh, Santa Cruz, Calif.
Sandra Chung, who wrote her master’s thesis on microbial drinking water quality at the University of North Carolina School of Public Health, shines a spotlight on waterborne germs:
Many municipal wastewater treatment plants use ultraviolet, or UV, light to disinfect wastewater. The particles in raw sewage absorb or scatter UV light and make it less effective, so UV disinfection usually happens after crude steps like settling and filtration remove most of the solids from the water. UV light disinfects by penetrating the outer membranes of bacteria and viruses and frying the DNA inside. Massive DNA damage kills the microbes or prevents them from reproducing; either way, they’re unlikely to make you sick.
UV light is simpler to use than chlorine, and it doesn’t change the way water tastes or smells. But it’s expensive and requires a lot of energy to do on a large scale. If you have time to spare in a sunny climate, you can leave drinking water in clear plastic bottles on a hot tin roof or other reflective surface. After six or more hours in direct sunlight, a healthy dose of solar UV and heat should kill most of the harmful bacteria in the water.
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