Water stains form on cement when it is exposed to a continuous source of moisture, such as a leaky faucet, a flower pot, damp laundry or a leaky seal around a plumbing fixture. These stains result from a buildup of minerals found in most untreated water supplies. Mineral stains are difficult to remove using simple soap-and-water techniques but, luckily, there are two easily available options.
Apply undiluted white vinegar to the entire mineral deposit you are attempting to remove and allow the stain to soak for approximately 20 minutes. Apply a second layer of white vinegar and scrub the stain with a stiff-bristled scrubbing brush vigorously for at least two minutes.
Rinse the area clean with fresh, cold water and dab it clean with a dry cloth. Allow the surface to air-dry. If you can still see a light mineral deposit ring, repeat these first two steps before continuing with Step 3.
Apply a generous amount of Lime-Away, as a last resort, to the mineral deposit if two attempts with the vinegar was unable to clear the stain. Lime-Away acts in a similar fashion to hydrochloric acid but with less danger. Allow the chemical cleaner to act on the stain for no longer than five minutes.
Put on a pair of vinyl gloves to protect your skin from coming into contact with the Lime-Away cleaner. Scrub the stain vigorously for about one minute, pouring cold water onto the stain while scrubbing to dilute the Lime-Away chemical. This dilution is necessary because Lime-Away itself can stain a surface if not diluted and rinsed off. Rinse the area well with water. Since Lime-Away can stain and discolor cloth, soak up the diluted Lime-Away with paper towels and discard according to directions on the bottle's label. Your stain should now be completely removed.