Ultraviolet (UV) light has become an established water treatment disinfection technology due to its extremely effective ability to kill or inactivate many species of disease-causing microorganisms. Ultraviolet light disinfection is effective on bacteria, protozoan parasites (e.g. Giardia, Cryptosporidium), and can also be effective for most viruses, providing sufficiently high UV dosage rates are used.
Disinfection is the reduction of harmful (=pathogenic) microorganisms to a concentration which is not harmful anymore. Typical UV disinfection systems involve the flow of water through a vessel containing UV lamps . As the water passes through this vessel, microorganisms are exposed to intense ultraviolet light energy which causes damage to genetic molecules (i.e. nucleic acids: DNA or RNA) needed for reproductive functions. This damage prevents the microorganism from multiplying or replicating in a human or animal host. Because the microorganism cannot multiply, no infection can occur. Disinfection of water is achieved when UV light causes microbial inactivation.