Water is a very complex fluid. It retains a little bit of practically everything that it contacts; the air while falling as rain, the earth as it percolates into the ground, the piping as it is transported and all kinds of organic and inorganic matter it may contact in its series of uses. Dissolved minerals in the water that can be either positively or negatively charged with electrons. The positive ions are called cations and the negative ions are called anions. It is these positive cations in the form of calcium, magnesium, iron and manganese that cause the hardness that is associated with water. Removal of these hardness ions via ion exchange is the process used for softening water.
The ion exchange process requires a resin tank and brine tank as a simple design requirement. Brine is educted into the mineral tank and washes over the resin in the mineral tank. Since the resin has a salt splitting capability an a cation accepting characteristic, sodium ions of the sodium chloride (brine= solution are attracted to the resin beds. This is called the regeneration process and it will continue until most of the exchange sites have been occupied with the sodium ions.
As the complex raw water enters the tank, the positive hardness ions exchange on the resin and displace the sodium ions to the service stream. Because calcium and magnesium are positive cations, the resins, being charged with positive sodium ions, will exchange with the calcium and magnesium ions. Calcium and magnesium will now occupy the exchange sites on the resin beds. This process will continue for a length of time until the hardness ions begin to leak out of the bottom of the resin bed. For all practical purposes, the resin is exhausted with calcium and magnesium and has no more sodium available do displace. This is the point where the softener must be regenerates.