In civil and industrial use the excessive quantity of limestone in the water causes some unpleasant and onerous inconveniences. The softening process takes place thanks to an exchange between sodium ions, fixed on particular resins, and calcium and magnesium ions contained in the water. This continuous exchange transforms normal water into softened water. When all the sodium ions have been exchanged, the cycle is terminated. To give resins a new efficiency, it is necessary to regenerate with sodium chloride (cooking salt).