What exactly is "hard" water?

A friend mentioned putting in a water softening system and though I've heard about "hard" water and water softeners... and have a general idea of what that means... I wasn't certain what actually made it "hard". What a perfect Daily Doodle topic!

Water can be soft or varying degrees of hard. Hard water does not describe the actual feeling of the water, instead, it is called hard water because it has has mineral deposits like calcium and magnesium within the water molecules. Soft water doesn’t have any type of mineral deposits within it, just H2O molecules.

Water doesn’t start out containing minerals. When it rains, that water is considered soft water. As the water seeps into the ground and absorbs calcium and magnesium, it becomes hard. According to U.S. Geographical Study research, Arizona, Texas and Utah have some of the hardest water in the United States. When tested, the minerals within the water were above 180 milligrams per liter. In the USGS’s scale of the softest water to hardest water, anything above 180 milligrams is the hardest water on the scale. Nevada and Idaho have water that is between 121 and 180 milligrams of minerals per liter.

Depending on the hardness of your water, after using soap to wash your hands you may have felt like there was a film or residue left on your hands. With hard water, soap reacts to the calcium to form "soap scum". When using hard water, more soap or detergent is needed to get things clean, be it your hands, hair, or your laundry. Cloudy dishes out of the dishwasher are mostly likely due to hard water. When hard water is heated, such as in a home water heater or kettle, solid deposits of calcium carbonate can form. This scale can reduce the life of household equipment, raise the costs of heating the water, lower the efficiency of electric water heaters, and clog pipes. And, yes, mineral buildup will occur in your home coffee maker too, which is why some people occasionally run vinegar (an acid) through the pot. The acidity of vinegar helps to dissolve mineral particles.

But hard water can have some benefits, too. Humans need minerals to stay healthy, and the World Health Organization (WHO) states that drinking-water may be a contributor of calcium and magnesium in the diet and could be important for those who are low on calcium and magnesium intake.

You likely know already if you have hard water or not, but one way to check is to fill a clear glass with tap water. Soft water will be clear with lots of bubbles on the surface of the water. Hard water on the other hand with look cloudy at first from the tiny bubbles in the water rather than on the surface.