Hardness

The minerals in hard water can cause deposits called scale in water pipes.

Waters that contain a significant concentration of dissolved minerals like calcium, magnesium, strontium, iron, and manganese, are called "hard" because it takes a large amount of soap to produce a lather or foam with these waters. When hard waters are heated in water heaters, hot-water pipes, and boilers, for example, they leave a mineral deposit called "scale."

Total hardness is expressed as mg/L of calcium carbonate because calcium (Ca^-2) and carbonate (CO₃^-2) are the dominant ions in most hard waters. The following table gives the concentration of CaCO₃ dissolved in water by its degree of hardness.

Hardness in the Red River
The graph shows the total hardness for the Red River in the Fargo-Moorhead (FM) metropolitan area for the period of April 2000 to March 2003. Hardness over that period ranged from below 200 to over 400 mg/L. This would put the Red River water in the "very hard" category. Hardness does not present a health concern, but softer water is easier to use and easier on equipment than hard water. At the local water treatment plants, the "very hard" water from the Red River is "softened" to the "moderately hard" level before it is made available to households, businesses, and industries in the FM area.

Graph of hardness (mg/L of calcium carbonate) for the Red River in the FM metro area for the period April 2000 to April 2003 in relation to the U.S. Geological Survey water hardness categories.