Contrary to what you might think, the dishwasher salt It’s not meant to make plates and glasses shinier, but to avoid limescale encrustations which tend to deposit on the dishes during washing. In fact, home water contains calcium salts (especially the limestonewhich is essentially calcium carbonate) e magnesium which can form clearly visible encrustations especially on pans and pots. To avoid this inconvenience, but above all to preserve the efficiency of the dishwasher and to avoid possible damage due to the accumulation of limescale on the internal components, this appliance is equipped with a water softenera device that decreases the water hardness replacing the calcium and magnesium ions dissolved in the water with ions of sodium. Where does this sodium come from? From the sodium chloridethat is, salt precisely, which therefore serves as “sodium tank” which regenerates the ion exchange resins present in water softeners. The use of salt is therefore recommended especially in areas where the water is particularly “hard”.
How the dishwasher reduces limescale: ion exchange water softeners
Dishwasher softeners they are not filters that retain encrusting salts: what they do is exchange ions of calcium (approx2+) and magnesium (Mg2+) dissolved in water with sodium ions. This is why they are called ion exchange water softeners. Inside them there are special resins containing sodium, in which the chemical process takes place ion exchange: these resins absorb the ions that form encrusting salts and replace them with sodium ions (Na+), whose salts are not encrusting.
Before being used for washing dishes, the water enters the softener, passes through the resins and the ion exchange lowers its hardness, that is – to simplify – its content of calcium and magnesium salts, making it “sweeter” (hence the name “softener”).
What is salt in dishwashers for: regenerating the water softener
As the softener does its work, the sodium in the resins is progressively consumed: a regular “replenishment” of sodium is therefore needed so that the device can continue to soften the water. This is exactly where the salt: as can be seen from its chemical formula (NaCl), half of its atoms are sodium! Salt is therefore a very economical and easily supplied source of sodium.
But how does the dishwasher extract sodium from salt? When we pour salt into the dishwasher, it is diluted in a brine solution in a special container. When the sodium in the resins is about to run out, a valve opens which allows the solution to enter the softener, where it passes through the resins which “capture” the precious sodium ions, releasing the calcium and magnesium ions accumulated with use. At this point the brine is expelled through drainage pipes. This process is called in jargon regeneration of the water softener.
Having the “softest” water possible is important not only to avoid limescale encrustations on plates and glasses, but also to ensure that limescale does not accumulate inside the dishwasher, where in the long run it can cause efficiency losses, decrease in quality of washes or malfunctions. In fact, therefore, salt is not only used for dishes but above all as a cooking tool dishwasher maintenance.
Can you use common table salt or coarse salt? Properties and composition
The salt sold as a specific product for machine washing is substantially identical to salt for food use (we are always talking about sodium chloride), with the difference of greater degree of purity. This is an important factor because the impurities in the salt can create, especially in the long term, accumulations that deteriorate the functioning of the dishwasher. Dishwasher salt is therefore more refined table salt, with a lower content of carbonates, iron and other substances.
According to FAO guidelines, table salt must be at least pure 97%while for dishwashers the 99% as a minimum purity threshold to avoid damage to the water softener. Using edible salt instead of specific salt could therefore constitute a risk risk.
