Let's get back to the "under sink water filter". My coach, the double kitchen sink has a conventional faucet for both half's and a "goose-neck" on the side. My in-line filter was removable (have to do that when winterizing)...and CAME with a PVC "jumper" pipe with fittings that fit just fine.
I never replaced the filter...felt there was no reason to. And...I think I'm right. Running coast to coast (NJ to CA.) 5 times and down to Florida 4 times, never got sick or had the least ailment to "bad" tap water from anywhere. Yes...sometimes it tasted different, but, as far as i am concerned is just as good as one of the biggest $ fraud ever put on the American public...bottled water. (my opinion)