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See also: Water softening. Soft water is surface water that contains low concentrations of ions and in particular is low in ions of calcium and magnesium. Soft water naturally occurs where rainfall and the drainage basin of rivers are formed of hard, impervious and calcium poor rocks.ecause soft water has few calcium ions, there is no inhibition of the action of soaps and no soap scum is formed in normal washing. Similarly, soft water produces no calcium deposits in water heating systems. Water that is not soft is referred to as hard water.
Hard Water Definition. Hard water is water that contains high amounts of Ca 2+ and/or Mg 2+ . Sometimes Mn 2+ and other multivalent cations are included in the measure of hardness.Note water may contains minerals and yet not be considered hard, by this definition.ccording to the USGS, the hardness of water is determined based on the concentration of dissolved multivalent cations: 1  soft water - 0 to 60 mg/L (milligrams per liter) as calcium carbonate. 2  moderately hard water - 61 to 120 mg/L.