Ultra violet disinfection is the most common method of protecting against microbiological contamination. The UV is normally the last piece of equipment in a treatment system to ensure it has the fully treated water giving the highest level of light transmission possible. The correct sizing of the UV is vital to ensure the correct dose and contact time. A correctly sized UV is very effective at killing bacteria E.coli, Coliforms etc. and is safer than introducing chemicals which would also alter the waters taste. Discoloured water can lower the UVT (Ultra Violet transmittance) which reduces the effectiveness of the UV. A UV lamp must be changed as a minimum every 12 months and the UV quartz sleeve checked periodically to maintain light transmission.