If you worry about the harmful microorganism in you tank that you need UV to control them, you should stop them at the first place. It is much more effective to sterilize your tank with bleach and be done with it.
We have well water at home, I shocked the well when we first move in. After 20 years, when we send the water for testing. There is absolutely no bacterial growth.
I always drink from the tank, and never buy bottle water except for emergency
use. It is costly and wasteful.