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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.
The most common treatment applied to hard water is ion exchange, aka water softening. In a water softener, the bad ions (minerals) are taken out of the water while softer ions are returned to it. This process is an almost equal exchange: there are still as many minerals in the water after water softening as before, but the water is now softer. It will, of course, still cause some scale buildup, as the soft dissolved minerals can still precipitate out.