Hard water stains are alkaline, so an acid-based cleaner is the best way to clean them. Cleaners with phosphoric acid works well and are safe for most surfaces. You can also get lime scale removers at janitorial supply stores, these contain 8 percent to 12 percent acid to get the job done a lot faster... most cleaners are 4 to 6 percent. The higher concentration of acid is safe on most surfaces as long as you rinse the surface to remove all trace of the acid once you are done.

Apply the cleaner directly to the stain. Let the acid sit for a few minutes after you apply it. Tough deposits may take more than one application. Scrub the applied areas with a white, scrub sponge (don't use colored scrubbers as the color may end up on the surface). Once done, rinse completely with clean water.

Make sure you read any manufacturer's warnings before applying phosphoric acid solutions to surfaces in your home.