2. Techniques for improving drinking water

2.1 Softeners

A water softener is a device that reduces water hardness by promoting the interaction of calcium and magnesium ions with sodium ions. A softener is not the same as an antiscalant, which does not remove limescale.

• A water softener works thanks to a resin on which sodium ions (Na+) are fixed. The calcium ions (Ca2+) in hard water are exchanged for Na+ ions as they pass through the resin. When all the Na+ ions in the resin have been used up, the softener needs to be regenerated. In this case, a saturated salt solution (sodium chloride NaCl) rich in Na+ ions is added. Calcium ions (Ca2+), on the other hand, are flushed down the drain with the rinse water.

• There are advantages and disadvantages...