Hardness in Drinking Water

Hard water (high in calcium and magnesium) is not a health risk. The calcium and magnesium in water can contribute positively to your overall mineral intake. An 8-ounce glass of moderately hard water contains about 50 to 75 mg of calcium. In comparison, an 8-ounce glass of milk provides about 300 mg of calcium.

Hard water can also be a nuisance at home because of:

• Gray staining of washed clothes
• Scum on wash and bath water after using soap or detergent
• Reduced lathering of soaps
• Buildup of scale on heating elements and boilers
• Reduced water flow in hot water distribution pipes due to scale buildup
• Accumulation of whitish-gray scale in tea kettles and other containers used to boil water

Hardness minerals can be removed with a water softener, which replaces the calcium and magnesium (and iron, manganese, radium and other positive ions) with sodium. High levels of sodium in drinking water may harm your health.

If you or someone in your household is on a low-salt diet, talk with your health care provider about the level of sodium in your water. The U.S. Environmental Protection Agency recommends no more than 20 mg/L (milligrams per liter) of sodium in drinking water for people restricted to a total sodium intake of 500 mg/day (milligrams per day). If you are concerned about your sodium intake but would like soft water for your appliances and plumbing, you can have your kitchen cold water faucet bypass the water softener.

Calcium and magnesium are naturally found in the Earth's crust. When rainwater combines with carbon dioxide from the air, it creates slightly acidic water. As rainwater moves through natural rock formations underground (usually limestone), it can dissolve the calcium and carry it into aquifers that serve as sources of drinking water.

High levels of calcium in drinking water mean you have “hard water.” Hard water can cause laundered clothes to look dingy. Hard water also causes a whitish-gray scale to form on glass shower doors and bathroom and kitchen fixtures.

The Health Department recommends testing your well or spring for hardness as part of an inorganic chemical test kit every five years. You can order the inorganic chemical test (Kit C) from the Health Department Laboratory, or you can use another certified drinking water lab to test for hardness.

There is no health standard for hardness in water. Hardness levels greater than 150 mg/L are considered hard water. Hard water is considered a nuisance and not a health issue.

Note: If your water is hard, it can reduce the efficiency of any type of water treatment, such as ultraviolet (UV) light treatment or a reverse osmosis (RO) system. You may need to also consider softening your water before installing water treatment systems.

Need help understanding your drinking water test results? Find out how to read your results

The most common way to remove hardness from drinking water is to install a water softener. For every milligram of hardness that is removed, 0.46 milligrams of sodium will be added to the water. Potassium chloride can be used as an alternative to sodium chloride, but potassium chloride is not as efficient at removing hardness.

Consider the location of nearby water sources before disposing of the wastewater produced by a water softener. The wastewater could contaminate nearby wells with sodium, so underground disposal should take place downhill and as far as possible from the well.

Hard water can cause scale on reverse osmosis treatment membranes and ultraviolet light bulbs, which can make treatment less effective. A water softener can resolve this problem.

The membrane manufacturers will often specify what the maximum hardness concentration can be, but the industry rule of thumb is that hardness should not exceed 120 to 170 mg/L (7 to 10 grains per gallon).

Learn more about water softeners

Funding is available to help you pay for water treatment or to fix your water system. Learn more about financial assistance programs and eligibility.