Madison's tap water is considered to be “very hard,” because of the minerals such as calcium and magnesium in the rock formations from which we draw water. This water contains 18-20 grains of hardness per gallon. There are no harmful health effects associated with these minerals (in fact, some believe they are beneficial), but measuring them does provide a guideline as to how water use may be affected. For example, hard water does result in more scale buildup and you need to use more soap and detergents. If you choose a water softener, it's recommended that a separate, unsoftened supply of water be kept for cooking and drinking. Ion exchange water softeners remove hardness by replacing the calcium and magnesium with sodium salt.
Also, when you buy a new appliance, such as a dishwasher, the manufacturer often makes reference to water hardness. This is because hard water can cause automatic dishwashers to leave film on dishes and build-up of minerals on mechanical parts. It may also cause washing machines to leave residue on articles of clothing and scales that clog water pipes or foul appliances such as water heaters.