Fill a spray bottle with a 50/50 solution of Dawn dish soap and vinegar. Spray it on the hard water stains and let it work. If they are tougher stains, you may have to scrub with a plastic scrubbie!
Spray with a soap scum remover such as scrubbing bubbles or lysol power bath and let sit for several minutes. Wipe gently with a soft nylon scrubby (white or pink) then rinse. To prevent buildup, spray, let sit and rinse weekly. No scrubbing required