How to Remove Hard Water Deposits. Hard water deposits form when tap water evaporates and leaves behind minerals such as calcium and magnesium.
Remove excess dirt, grime or mildew from the area requiring cleaning.
Apply an acid cleaner, such as one containing phosphoric acid, to affected areas. Specifically, use a vitreous enamel cleaner on enameled surfaces or a cream cleaner on acrylic surfaces.
Consider an alternative: Try wiping the area with liberal amounts of white vinegar. Leave the area for 30 minutes and allow the chemicals to break down the hardened mineral deposits.
Rinse the chemically treated area thoroughly.
Reapply the cleaner for a longer period of time if deposits are extreme and don't respond to an initial treatment, then scrub with a razor blade or steel wool.