Hard water
Water with high mineral content that leaves scale on pipes and fixtures.
Hard water carries dissolved calcium and magnesium picked up from rock and soil. It's not a health risk, but it's hard on your home: it leaves chalky scale on faucets and showerheads, builds up inside pipes and your water heater, makes soap hard to lather, and spots glassware. The scale forces your water heater to work harder and shortens its life. A water softener removes the minerals; a yearly water-heater flush clears the sediment hard water leaves behind.