pass by.. cincai google and saw these info:

UV light is only capable of killing microorganisms in the water such as bacteria, viruses, molds, algae, yeast, cryptosporidium and giardia. Therefore, the main purpose is to process water that has not been chlorinated or disinfected by chlorine or other chemicals.

http://www.freedrinkingwater.com/whole-hou...hlorination.htm

Conclusion-
The safest least expensive way to control microorganisms in well water is to use chlorine (sodium hypochlorite also known as bleach) for disinfection.

http://www.awqinc.com/wp-content/uploads/2...orination_1.pdf