I have had similar thoughts. Our agency (A Florida County government department) treats wastewater to advanced waste treatment (AWT) standards thru biologic action followed by high level disinfection. The resulting effluent (we call it reclaimed water) is very good (meets State and Federal drinking water standards) and is used for landscape irrigation. We also did R&D for awhile with aquifer storage and recovery (ASR) of the same product. In so doing we had to pass our product thru dual in-line UV reactors to inhibit coliform, protozoa, and giardia (re)growth. This worked out quite well; alas, our geology was bad so our storage and recovery R&D did not work out.
The ultimate answer to your question depends upon what you are really looking for as a final product. How you get to the end depends upon what you start with.