When the raw water containing hardness ions passes through the sodium resin in the exchange tank, Ca2+ and Mg2+ in the water are adsorbed by Na+ exchange in the resin, removing Ca2+ and Mg2+ to remove carbonate or non-carbonate hardness, that is, softening water. After the resin adsorbs a certain amount of Ca2+ and Mg2+, it must be regenerated. The regeneration is to flush the resin layer with the salt water in the salt tank. Na+ in the brine replaces the hardness ions on the resin into the water, and is discharged out of the tank with the regeneration liquid. Restore resin exchange capacity and continue to soften water production.