As others have noted here, ...

Published August 10, 2018 20:35 by Terry Hughes CWS, CI, UV-CI, Problem Water and Technical Service Specialist at Culligan of Denver, a div. of Halls Water

As others have noted here, the water supply must be relatively low Hardness, Iron, Manganese, Minerals or Metals that may coat the Quartz Sleeves, and they will still require a regular cleaning schedule. Suspended Sediments, Collodials or Tannins which will block the UV transmittance through the Reaction chambers. And there is no downstream residual disinfection. For a pipeline supply, it would be recommended to have a disinfectant injected post UV.

The upside is that UV with the proper sizing, dosing, and flow , WILL deactivate even the toughest Protozoans, Bacteria, and Viruses! Also amounts of residual disinfectants needed are substantially reduced.