Salt water tank is used in conjunction with sodium ion exchange resin tank. Sodium ion exchange resin can remove calcium and magnesium ions from water by exchange. After a period of time, sodium ions on sodium ion exchange resin are exchanged and lost. Sodium ion exchange resin should be regenerated through salt water in salt water tank. The regenerated sodium ion exchange resin can resume its exchange capacity and continue to be used. When the salt in the brine tank is used up, the reclaimed salt should be replenished in time.