Thanks Craig. I will agree to disagree on this point....if my TDS showed 35-50 I would be replacing filters immediately. With a TDS that low you may have a longer filter life, if you ever wanted to go the RO/DI route. The stripped water (RO/DI) wants the phosphates, and that is how it would wash them away. Tap water would only make it wet - not take away the phosphates. Anyway, just some thoughts.