The killing action is the same as that provided by sunlight in open streams and ponds. Importance of A Disinfectant Residual UV has not gained widespread acceptance in the public water supply field, due to its lack of a disinfectant residual. A residual has been considered important in the US to conclusively demonstrate that all water passing through a disinfection device was in fact disinfected. In Europe, the residual issue is judged as less important and UV is used more frequently. Currently in the U.S., UV use is limited to small nonpublic systems such as private home wells, surface water supplies at lakeside homes and many industrial, medical and food processing applications.
Ocean liners use on-board UV systems while at sea.
The State of New Hampshire does not allow the use of UV light for final disinfection of public water systems, that require disinfection, because of the lack of a disinfectant residual. The US EPA is currently reevaluating their policies concerning UV disinfection of public water supplies. How Ultraviolet Disinfection Works UV disinfection devices expose the raw water to light from a special lamp which produces UV radiation at 253 nanometers. The UV light must come in contact with each microorganism to be effective. Therefore, suspended particles such as turbidity or iron and manganese precipitates would prevent the UV from achieving total kill of the organisms.