hard water

water containing a high concentration of minerals and calcium

Hard water is water that has a high mineral content (contrast with soft water), usually consisting of calcium (Ca2+) and magnesium (Mg2+) ions, and possibly including other dissolved metals, bicarbonates, and sulfates. Calcium usually enters the water as either calcium carbonate (CaCO3) in the form of limestone and chalk, or calcium sulfate (CaSO4) in the form of other mineral deposits. The predominant source of magnesium is dolomite (CaMg(CO3)2). Hard water is generally not harmful.
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Alkaline water containing dissolved salts that interfere with some industrial processes and prevent soap from sudsing.

Compare with water softener .Hard water is water contaminated with compounds of calcium and magnesium. Dissolved iron, manganese, and strontium compounds can also contribute to the "total hardness" of the water, which is usually expressed as ppm CaCO3. Water with a hardness over 80 ppm CaCO3 is often treated with water softeners , since hard water produces scale in hot water pipes and boilers and lowers the effectiveness of detergents.

Noun
1. water that contains salts (as calcium and magnesium ions) that limit the formation of lather with soap
(hypernym) water, H2O