The growing environmental awareness setting standards regarding water quality and enhancing the water re-use, had lead UV treatment to rapidly become a "must" treatment on several water streams.

The UV light can be considered as electromagnetic radiation with a wavelength ranging from 10 to 400 nm. Ultraviolet irradiation (UVC) is an efficient water disenfectant due to its ability to deactivate or kill waterborne pathogens up to 99.99%, by changing the DNA, thus the cell division of the microorganism is interrupted - it can no longer reproduce itself and therefore loses its pathogenic effect. UV light is effective against bacteria (e.g. Clostridium) and viruses, however, it was recently investigated that UV is also effective against Cryptosporidium and Giardia, both as microorganisms and as their modifiec cells which are resistant to chlorine.

The installation of a UV system should be immediately after filters, ozone addition or other partical removal applications since then, the clarity (UVT) of water is at its maximum. Additionally, a UV system is usually built in prior to chemical addition since in most cases, residual disinfection is needed.

Ultraviolet light is commonly applied as a secondary process in drinking water applications, secondarily treated effluent from water treatment plants, aquaculture, swimming pool water facilities. UV-based treatments accomplish efficient and rapid cleaning of the water without leaving any residual disinfectant behind.