Mix equal parts white vinegar and water in a spray bottle. Spray the solution onto the hard water stains and let it sit for a few minutes. Scrub with a brush or sponge, then rinse thoroughly.
Cut a lemon in half and rub it directly onto the hard water stains. The citric acid in the lemon will help dissolve the mineral deposits. Rinse and wipe clean.
Make a paste using baking soda and water. Apply the paste to the stains and let it sit for a few minutes. Scrub with a brush or sponge, then rinse and wipe clean.
There are various commercial cleaners designed specifically for hard water stains. Follow the manufacturer's instructions for best results.
Mix a small amount of dish soap with vinegar. Apply the mixture to the stains and scrub with a brush or sponge. Rinse thoroughly.
Apply a small amount of rubbing alcohol to a clean cloth. Rub the cloth onto the hard water stains until they dissolve. Rinse and wipe clean.
Make a paste using equal parts hydrogen peroxide and cream of tartar. Apply the paste to the stains and let it sit for a few minutes.