Seriously, I caught a podcast where a skin doctor talked about hard water. She said the minerals can leave a real film on your skin that doesn't rinse off easy. That gunk can throw your skin's balance out of whack and make it feel rough. But a simple filter probably handles chlorine, which is another MAJOR irritant. So hard water might not be the only villain, but it's for sure a factor for some.
For years, I brushed off hard water complaints as mostly hype. Then my cousin moved to a town with terrible water and her chronic redness cleared up after installing a softener. That film wadereed mentioned is real; it stops soap from rinsing clean and leaves residue. It's not everyone's issue, but for some, hard water is a big piece of the puzzle.