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'Hard water is water that has high mineral content (in contrast with soft water). Hard water has high concentrations of Ca2+ and Mg2+ ions. Hard water is generally not harmful to one's health but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling towers, and other equipment that handles water. In domestic settings, the hardness of water is often indicated by the non-formation of suds when soap is agitated in the water sample."