Disinfection

is carried out to inactivate pathogens (bacteria, viruses, and protozoa—see wastewater). Commonly used disinfectants include chlorine (and its derivatives), ultraviolet (UV) light, and ozone. Chlorine and its derivatives are used to disinfect drinking water because they provide residual disinfection that protects the water as it goes through the pipes to homes and businesses. There are some concerns about the potentially health-damaging byproducts from chlorine disinfection. This risk is minimal, however, if the water is filtered and clear before it is disinfected. UV light (which occurs naturally in sunlight or is generated from special lamps) and ozone are increasingly being used to disinfect treated water. They do not provide residual disinfection, so chlorine is normally added after treatment with UV light or ozone.