Ultraviolet (UV) light from the sun kills microbial DNA and in some countries huge lagoons have been constructed as a natural means of purifying water and treating effluent from sewage systems. Adopting the same principle, Jersey has installed a UV irradiation plant, consisting of nine banks of 144 lamps suspending in the effluent flow at a sewage treatment works near St Helier. Only a very small dose of UV light is needed, and the radiation treats a maximum flow of 1000 litres a second, killing 99.99% of faecal microbes, preserving the safety of bathers on the coastline without damaging island marine life with conventional chlorine or other chemical disinfectants.