UV radiation can be an effective viricide and bactericide. Disinfection using UV radiation is commonly used in wastewater treatment applications and is finding an increased usage in drinking water treatment. Many bottlers of spring water use UV disinfection equipment to sterilize their water. Solar water disinfection is the process of using PET bottles and sunlight to disinfect water. Ultraviolet germicidal irradiation is the generic process to inactivate microorganisms in water, air, medical environments, etc.

http://en.wikipedia.org/wiki/Ultraviolet#Disinfecting_drinking_water