Hardness in Groundwater

WATER STEWARDSHIP INFORMATION SERIES
Hardness in Groundwater
February 2007
What is water hardness?
Water hardness is primarily the amount of calcium and magnesium, and to a lesser extent, iron in the water. Water hardness is measured by adding up the concentrations of calcium, magnesium and converting this value to an equivalent concentration of calcium carbonate (CaCO
3
) in milligrams per litre (mg/L) of water. The Guidelines for Canadian Drinking Water Quality Hardness divide hardness into the following categories:
Hardness Category
Equivalent Concentration of CaCO
3
Soft
< 60 mg/L
Medium hard
60 mg/L to < 120 mg/L
Hard
120 to < 180 mg/L
Very hard
180 mg/L or greater
The optimum range of hardness in drinking water is from 80 to 100 mg/L. Water with hardness greater than 200 mg/L is considered poor in most regions of the province and water with hardness greater than 500 mg/L is normally considered unacceptable for domestic purposes. On average, water in British Columbia has been found to range in hardness from less than 10 mg/L to 180 mg/L. Groundwater tends to be harder than surface water and can range to greater than 1000 mg/L.
What are the known sources of water hardness?
Water hardness in most groundwater is naturally occurring from weathering of limestone, sedimentary rock and calcium bearing minerals. Hardness can also occur locally in groundwater from chemical and mining industry effluent or excessive application of lime to the soil in agricultural areas.
What are the environmental health concerns?
Hard water is mainly an aesthetic concern because of the unpleasant taste that a high concentration of calcium and other ions give to water. It also reduces the ability of soap to produce a lather, and causes scale formation in pipes and on plumbing fixtures. Soft water can cause pipe corrosion and may increase the solubility of heavy metals such as copper, zinc, lead and cadmium in water. In
some

References: magnesium in drinking-water: public health significance (WHO, 2009) moderately hard; 120–180 mg/l, hard; and more than 180 mg/l, very hard (McGowan, 2000) ates (National Research Council, 1977). HARDNESS IN DRINKING-WATER drinking 2 litres of water per day (Neri et al., 1985). 2.2 Food the order of 50% (Ong, Grandjean & Heaney, 2009). For calcium and magnesium, the typical contribution from water is 5–20% (WHO, 1973; National Research Council, 1977; Neri & Johansen, 1978). Because of dietary habits in most countries, many people fail to obtain the