I'll tell you something else I just found out about using pumice stone. If you get the hard water rings around your toilet bowl that you can scrub and scrub and scrub and can't seem to totally eradicate, use a pumice stone. It's softer than the porcelain, so it can't scratch the surface, but it's harder than the water deposits. Now, I need to go get a new pumice stone to put back in the shower.