General Information: Water hardness is commonly defined as the sum of the polyvalent cations dissolved in the water. The most common such cations are calcium and magnesium, although iron, strontium, and manganese may contribute (AWWA, 1990; EPA, 1986). Hardness is usually reported as an equivalent quantity of calcium carbonate (CaCO3). Generally, waters are classified according to degree of hardness (EPA, 1986). The hardness of your water will be reported in grains per gallon, milligrams per liter (mg/l), or parts per million (ppm). One grain of hardness equals 17.1 mg/l or ppm of hardness.
The Environmental Protection Agency (EPA) establishes standards for drinking water which fall into two categories -- Primary Standards and Secondary Standards. Primary Standards are based on health considerations and Secondary Standards are based on taste, odor, color, corrosivity, foaming, and staining properties of water. There is no Primary or Secondary standard for water hardness. Water hardness is classified by the U.S. Department of Interior and the Water Quality Association as follows:
Classification mg/l or ppm grains/gal Soft 0 - 17.1 0 --1 Slightly hard 17.1 - 60 1 - 3.5 Moderately hard 60 - 120 3.5 - 7.0 Hard 120 - 180 7.0 - 10.5 Very hard 180 & over 10.5 & over
NOTE: Other organizations may use slightly different classifications. This information can be found at http://wilkes.edu/~eqc/hard1.htm#results.
Hardness is primarily a function of the geology of the area with which the surface water is associated. Waters underlain by limestone are prone to hard water because rainfall, which is naturally acidic because it contains carbon dioxide gas, continually dissolves the rock and carries the dissolved cations to the water system.
Numerical Categories: Limits: Designated Use Limit (mg/l CaCO3) Industry (raw water source) (EPA, 1986) Textile 120 max concentration Pulp and paper 475 max concentration Chemical 1,000 max concentration Petroleum 900 max concentration Electric Utilities 5,000 max concentration
Health Effects: Not applicable
Environmental Effects: The effects of hardness on aquatic life is a function of the cations comprising the hardness.
Irrigation Effects: Carbonate deposits may clog pipes and coat the inside of water holding tanks. Extreme hardness may interfere with chemical processes.
(APHA, 1992; Nebraska Administrative Code, 1993)
Hardness, mg equivalent/L CaCO3 = ([Ca,mg/l]*2.497) + ([Mg,mg.l]*4.116)