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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.
Well water from areas which have a lot of limestone (calcium) is often hard. Water that comes from lakes and rainwater is often devoid of minerals, making it soft. It is important to understand how water hardness affects pH in your aquarium. Hard water (high mineral content) is usually high in pH. Soft water (low mineral) is usually low in pH. The mineral in hard water acts as a buffer that combats aridification in the water. The resulting water will be more alkaline and higher in pH.