Groundwater - Natural Characteristicsof Groundwater

As groundwater travels its course from recharge to discharge area, it undergoes chemical and physical changes as it mixes with other groundwater and reacts with the minerals in the sand or rocks through which it flows. These interactions can greatly affect water quality and its suitability or unsuitability for a particular use.

Minerals

Water is a natural solvent capable of dissolving other substances. Spring waters may contain dissolved minerals and gases that give them subtle flavors. Without minerals and gases, water tastes flat. The most common dissolved FIGURE 4.5
The Ogallala (or High Plains) Aquifer
SOURCE: "Figure 1," in High Plains Regional Ground Water Study, U.S. Geological Survey, http://co.water.usgs.gov/nawqa/hpgw/images/figure1.gif (accessed April 1, 2005) mineral substances are calcium, magnesium, sodium, potassium, chloride, sulfate, and bicarbonate. Water is not considered desirable for drinking if it contains more than 1,000 milligrams per liter (mg/l) of dissolved minerals. However, in areas where less-mineralized water is not available, water with a few thousand mg/l of dissolved minerals is used routinely, although classified as saline.

Some well and spring waters contain such high levels of dissolved minerals that they cannot be tolerated by humans, plants, or animals. In high concentrations, certain minerals can be especially harmful. A large quantity of sodium in drinking water is bad for people with heart disease. Boron, a mineral that is good for some plants in small amounts, is toxic to other plants in only slightly elevated concentrations. Such highly mineralized groundwater usually lies deep below the surface and has very limited uses.

Water Hardness

Water that contains a lot of calcium and magnesium is said to be hard. The hardness of water can be expressed in terms of the amount of calcium carbonate (the principal constituent of limestone) or equivalent minerals that would remain if the water were evaporated. Water is considered soft when it contains 0 to 60 mg/l of hardness constituents, moderately hard with 61 to 120 mg/l, hard with 121 to 180 mg/l, and very hard if more than 180 mg/l are present.

Very hard water is not desirable for many domestic uses, and leaves a scaly deposit on the insides of pipes, boilers, and tanks. Hard water can be made soft at a fairly reasonable cost, although it is not always desirable to remove all the minerals from drinking water since some are beneficial to health. Extremely soft water can corrode metals but is suitable for doing laundry, dishwashing, and bathing. Most communities seek a balance between hard and soft water in their municipal water systems whenever possible.