I have heard of soft water causing skin problems in humans because the surfactants in soaps will bind to the skin and cause rashes but I have never heard of hard water causing any skin problems. I know it plays hell on pipes and plumbing though. When I was a kid we use to catch turtles in a flooded limestone quarry. That would have been very hard water. I don't recall them having skin problems. Water that's hard because of high Ca (as opposed to Mg) might actually be a good thing. Some people add plaster of paris and cuttle bone to the tank as a source of Ca for shell development.