Hard water stains should be removable with vinegar; if that isn't strong enough, go for CLR or some other acidic product. I find that the best method for prevention of hard water build up, is to squeegee or swab with a towel after every shower. I have heard of people using car polish on the shower walls to prevent water stain build up. It might be worth a try.
Add your voice to the conversation. Click here to answer this question.