Water Hardness

Water Hardness

We often get calls about the hardness of our water. The simple definition of water hardness is the amount of dissolved calcium and magnesium in the water. Perhaps you may have noticed mineral deposits on your dishes, coffee pot, faucets/aerators or shower/bathtub.

Mineral deposits are formed by ionic reactions resulting in the formation of an insoluble precipitate. For example, when hard water is heated, Calcium (Ca2+) ions react with bicarbonate (HCO3-) ions to form insoluble calcium carbonate (CaCO3). This precipitate, known as scale, coats the vessels in which the water is heated, producing the mineral deposits on your cooking dishes.

Water systems using groundwater as a source are familiar with water hardness.

Water is a great solvent for naturally occurring minerals. As water moves through soil and rock it dissolves small amounts of these minerals. The Spokane Valley Rathdrum Prairie Aquifer moves through rock and sand deposits from Glacial Lake Missoula. These deposits contain naturally occurring minerals such as calcium and magnesium, giving us moderately hard water in the Spokane/Coeur d’Alene region.

These deposits are not harmful, but they may be frustrating to try to clean. Humans need minerals to stay healthy, and the National Research Council (National Academy of Sciences) states that hard drinking water generally con- tributes a small amount toward beneficial total calcium and magnesium hu- man dietary needs.

The District samples inorganic compounds annually at our water sources. In 2017 our samples measured 104 ppm of CaCO3 (27 ppm of Ca and 8.97 ppm of Mg). At 104 ppm our water is in the moderately hard classification (see hardness scale below).