Ultraviolet (UV) purification systems use UV light to disinfect water by inactivating microorganisms that can cause illness. UV light is a natural part of sunlight and is effective against viruses, bacteria, and protozoa. UV purification systems use UV light in the 250-270 nanometer (nm) range, with most systems operating at 254 nm. At this wavelength, UV light can penetrate microorganisms' cells and damage their DNA, preventing them from reproducing and infecting other organisms