The demineralization (or deionization) is a process able to almost completely remove the water salinity, through an ion exchange function through resins. The positively charged ions are called "cations", those with negatively charged "anions". The exchange can take place via successive passages on cationic and anionic resins, or in a single step of intimately mixed resins, in "mixed bed", each of which can produce different levels of quality of treated water. When the resins are saturated it is necessary to proceed to a regeneration with hydrochloric acid and caustic soda, to restore the exchange capacity.