Part of it depends on where you are doing the work.
UV light doesn't work well on hard water, as the bacteria can be behind the hardness. So then you would have to put the light after the softener, and thus run the 'dirty' water through the softener.

The chlorine would be in front of the softener, but I believe would require a filter to remove the chlorine (prior to softening if necessary).

In water and wastewater treatment plant that use UV systems the water being treated has to be rather clean as scale build up on the light tubes will lessen the UV rays. Cl2 is added before UV.

Cl2 will kill about 85% of bacteria, 60% of virii and about 70% of microorganisms. UV will take care of the others but good filtration is also required.

Why is there a coliform risk in your plumbing?

the guy from independent local lab , told us to just get a uv light.. supp our hardness is 12 or so... no way do I want chlorine in my water.... even lab guy says chlorine is bad cause it breaks down to into bad stuff.
So I guess we will have to clean uv glass more we we get a uv light.

Bacteria and other organism can't 'hide' behind hardness because it is dissolved. They hide behind turbidity or other matter in the water. hardness is bad for UVs because calcium deposits build up in the quartz lens and renders the UV penetration in a diminished strength and reduced effectiveness.

well cant we just clean the lens more often? just asking....
Jean

No, cleaning the quartz lens is neither practical or ever recommended. You mustn't even touch it with your bare hands. Sometimes a citric acid is used but this involves a complicated application process.

UVs on hard water have a very short life span. Do you understand the differences between NSF-Standard-55 Class-A and -B systems?