We call water "hard" if it contains a lot of calcium, magnesium or other minerals. Groundwater acquires these metals by dissolving them from surrounding soil and rock. Industry measures water hardness in terms of grains per gallon (GPG) or milligrams per liter (mg/L). A grain is defined as 64.8 milligrams of calcium carbonate [source: Business Dictionary]. If your water tests at 1 GPG (17.1 mg/L) or less, then you have soft water. Water around 1-3.5 GPG (17.1-60 mg/L) occupies a gray zone between soft and slightly hard water and 3.5-7 GPG (60-120 mg/L) is moderately hard. Hard water is around 7-10.5 GPG (120 - 180 mg/L), and very hard water is above that. Hard water causes two problems:
Dissolved calcium and magnesium precipitate out of hard water as scale, which builds up on the insides of pipes, tea kettles, coffee makers, water heaters,and fixtures. Scale reduces flow through pipes and is a poor conductor of heat. Eventually, pipes can become completely clogged.
Hard water reduces soap's ability to lather, whether in the sink, shower, dishwasher or washing machine, and reacts with soap to form a sticky scum. You can combat hard water in various ways, adding a packaged chemical softener such as powdered borax or washing soda (sodium carbonate), or running it through a water softener.
Filtration in sink taps and refrigerator water dispensers improves water's taste, but it’s impractical as a whole household solution. Packaged chemicals soften water in small batches, such as washing machine loads, but render the water undrinkable, take a toll on clothes, and, in some cases, contain phosphates that harm the environment.
A water softener removes the problem (minerals in the water), and are the least costly and most effective way to rid your water of troublesome minerals.