A UV water disinfection system is a point-of-entry unit that passes water past a UV-C lamp to inactivate bacteria, viruses, and protozoa by damaging their DNA. It kills germs without chemicals but does not remove chemicals or sediment, so it needs pre-filtration. It is common for treating well water.
A UV water disinfection system kills germs in water with ultraviolet light. Water flows past a UV lamp inside a sealed chamber on its way into the house. The light adds no chemicals and changes no taste. It is one of the most common ways to make well water safe to drink.
How UV light kills germs
The lamp gives off UV-C light, a short wavelength of ultraviolet energy. As bacteria, viruses, and protozoa pass close to it, the light damages their DNA. That damage stops them from reproducing. A germ that cannot reproduce cannot make you sick. This handles common threats like E. coli, Giardia cysts, and Cryptosporidium. The EPA lists ultraviolet light as one accepted way to disinfect a private well.
What UV does not do
UV light only deals with living germs. It does not remove chemicals, metals, hardness, or sediment. Cloudy water is a real problem. A speck of dirt can shade a germ and let it slip past the lamp untouched. For that reason UV needs clean, clear water to work. Most systems add a sediment pre-filter ahead of the lamp. An activated carbon filter or a reverse osmosis membrane can take out chemicals if the water needs it.
Standards and where it is used
A UV unit is a point-of-entry device. It treats all the water where the main line enters the home. That makes it popular for private wells and rural supplies. The main product standard is NSF/ANSI 55. Class A systems give a UV dose of 40 mJ/cm2 and are built to treat water that may be unsafe. Class B systems give 16 mJ/cm2 and only add backup protection to water already judged safe. For well disinfection, a Class A system is the right pick.