We have the "Water Fixer" 12V system. It works well. The first filter is a Pentek CP-5 micron pleated filter and the second one is a Pentek CBC-0.5 (nominal) rated carbon block filter. All water goes through the "Pentek system, including that which goes into the hot water tank. Then there is the UV filter. The water has no off flavours at all, and our water tanks had not undergone the "Headmistress" chlorine shock treatment until just yesterday.
The UV part of the system is manually controlled by a switch on the galley sink. We use that when we fill our Brita water filter that goes in the fridge. But, the Brita really doesn't contribute to the flavour of the water.
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Knowing how well it works, I would recommend. I think that pre-filtering water that goes into your tanks would be a pain in the grass as the process would be very slow and we have 350 gallon tanks. Personally, I think that periodically shocking the system plus the "Water Fixer" is preferable.