This is the common term for water containing dissolved metal salts, commonly calcium and magnesium, and sometimes iron and manganese. Laundry products usually contain water softeners to inactivate or remove these salts, allowing the detergents to work better.
Hard water also contaminates bathtub and shower surfaces due to the mineral deposits left behind when it dries. A good way to prevent this is to encourage everyone to spend a couple of minutes wiping down wet tub and/or shower surfaces with a dry terry towel after they finish bathing or showering. A plastic squeegee or 12-inch to 14-inch window squeegee is even faster on flat and perpendicular surfaces.
Severe mineral deposits need to be treated with acids formulated to break down mineral salts. Be sure to read all label instructions, cautions and warnings carefully before using any product containing acid. Common white vinegar (acetic acid) works well (although slowly) and is safe for home use.
See also Water softener.