UV Water Sanitation is by far the most important filtration process when it comes to rain water treatment. Rain water harbours bacteria of all types but is some cases much more harmful bacteria may be present in the tank.
E-Coli is a common bacterium in tank water and is due mostly to Frogs in and around your tanks/catchment. Ultraviolet sanitation works by breaking down the cell wall of a micro-organism allowing oxidation to occur which in turn prevents the bacteria from multiplying until it is finally eradicated. Ultraviolet filtration is a chemical free solution to water sanitation.