Hard water means the water has a high mineral content (e.g. calcium, magnesium, iron, etc.). This often results in whitish mineral deposits left on faucets, shower doors, drains, windows. Vinegar, a weak acid, can dissolve many of these deposits. Remove mineral deposits around faucets, cover deposits with strips of paper towels, soaked in vinegar. Let set for 1 hour and clean. -- from the U.S. Environmental Protection Agency
