Water is a good solvent and picks up impurities easily. Pure water - tasteless, colorless, and odorless - is often called the universal solvent. When water is combined with carbon dioxide to form very weak carbonic acid, an even better solvent results. As water moves through soil and rock, it dissolves very small amounts of minerals and holds them in solution. Calcium and magnesium dissolved in water are the two most common minerals that make water "hard." The degree of hardness becomes greater as the calcium and magnesium content increases.

Hard water interferes with almost every cleaning task, from laundering and dishwashing to bathing and personal grooming. Clothes laundered in hard water may look dingy and feel harsh and scratchy. Dishes and glasses may be spotted when dry. Hard water may cause a film on glass shower doors, shower walls, bathtubs, sinks, faucets, etc. Hair washed in hard water may feel sticky and look dull. Water flow may be reduced by hard water deposits in pipes. Dealing with hard water problems in the home can be a nuisance. The amount of hardness minerals in water affects the amount of soap and detergent necessary for cleaning. Soap used in hard water combines with the minerals to form a sticky soap curd. Some synthetic detergents are less effective in hard water because the active ingredient is partially inactivated by hardness, even though it stays dissolved. Bathing with soap in hard water leaves a film of sticky soap curd on the skin. The film may prevent removal of soil and bacteria. Soap curd interferes with the return of skin to its normal, slightly acid condition, and may lead to irritation. Soap curd on hair may make it dull, lifeless and difficult to manage. When doing laundry in hard water, soap curds lodge in fabric during washing to make fabric stiff and rough. Incomplete soil removal from laundry causes graying of white fabric and the loss of brightness in colors. A sour odor can develop in clothes. Continuous laundering in hard water can shorten the life of clothes. In addition, soap curds can deposit on dishes, bathtubs and showers, and all water and plumbing fixtures. Hard water also contributes to inefficient and costly operation of water-using appliances. Heated hard water forms a scale of calcium and magnesium minerals that can contribute to the inefficient operation or failure of water-using appliances. Pipes can become clogged with scale that reduces water flow and ultimately requires pipe replacement.

Hard water is not a health hazard. In fact, the National Research Council (National Academy of Sciences) states that hard drinking water generally contributes a small amount toward total calcium and magnesium human dietary needs. They further state that in some instances, where dissolved calcium and magnesium are very high, water could be a major contributor of calcium and magnesium to the diet. Hard water treated with an ion exchange water softener has sodium added. According to the Water Quality Association (WQA) the ion exchange softening process adds sodium at the rate of about 8 mg/liter for each grain of hardness removed per gallon of water. For example, if water has a hardness of 10 grains per gallon, it will contain about 80 mg/liter of sodium after being softened with an ion exchange softener if all hardness minerals are removed. Because of the sodium content of softened water and potential benefits of drinking hard water, some individuals may be advised by their physician not to install water softeners, to soften only hot water, or to bypass the water softener with a cold water line (usually to a separate faucet at the kitchen sink) to provide unsoftened water for drinking and cooking.

If you have a private water supply, you can have the water tested for hardness. Most water testing laboratories offer hardness tests for a fee. You may contact the University of Minnesota Extension Service-Dakota County in Farmington (651-480-7700) for information on procedures for testing private water supply. Many companies that sell water treatment equipment offer hardness tests. When using these water tests, be certain you understand the nature of the test, the water condition being measured, and the significance of the test results. An approximate estimate of water hardness can be obtained without the aid of outside testing facilities. Water hardness testing kits are available for purchase. If more accurate measurements are needed, obtain a laboratory test.

Water hardness often is expressed as grains of hardness per gallon of water (gpg) or milligrams of hardness per liter of water (mg/L). The table adapted from the Water Quality Association (WQA) below shows hardness classifications. Hardness ions are typically combined with sulfate, chloride, carbonate, or bicarbonate ions. For consistency, concentrations are generally converted to the equivalent concentration as calcium carbonate (CaCO3) and expressed in terms of hardness as calcium carbonate.

Summary
Hard water is not a health hazard, but dealing with hard water in the home can be a nuisance. The hardness (calcium and magnesium concentration) of water can be approximated with a home-use water testing kit, or can be measured more accurately with a laboratory water test. There are two ways to help control water hardness; add a packaged or liquid softener to a batch of water (washing machine or tub), or use an ion exchange water softening unit.