Certain kinds of ultraviolet (UV) light are very effective at killing bacteria, viruses, fungi and other undesirable organisms. Hospitals use special UV lights for sterilizing air and work surfaces. You can also purify water with UV light, as part of a larger process.
Source
Fluorescent lamps produce UV light. The fluorescent lamps used in homes and offices have a coating of phosphorous that absorbs UV and gives off useful white light. Without this coating, the lamps give off UV strong enough to kill germs.
Wavelength
Generally, UV light is a band of electromagnetic energy having wavelengths ranging from about 400 nanometers (nm) down to 1 nm. The most effective wavelengths for killing organisms in water is 265 nm.
Effectiveness
UV light destroys DNA and other organic molecules in bacteria and viruses, effectively killing the organism. UV kills microbes in a matter of seconds, though the light source must be sufficiently bright.
Turbidity
Dissolved solids that turn water dark will also block UV light, making it much less effective. For UV to work, the water must be reasonably clear.
Limitations
UV light's purifying power extends only to microorganisms. It cannot remove lead, chlorine, or harmful minerals from water. For this reason, it's best to use UV light as a final part of a multi-stage purification process.
