The typical water softener has two parts: a mineral tank and a brine tank. The mineral tank is filled with small polystyrene beads, also known as resin or zeolite. The beads carry a negative charge. Calcium and magnesium in water both carry positive charges. This means that these minerals will cling to the beads as the hard water passes through the mineral tank. The brine tank is filled with a brine solution created by adding common salt (sodium chloride) to water. Like calcium and magnesium, sodium ions have positive charges, although not as strong as the charge on the calcium and magnesium.
In normal operation, hard water moves into the mineral tank and the calcium and magnesium ions move to the beads, replacing sodium ions on the beads. The sodium ions go into the water. Once the beads are saturated with calcium and magnesium, the unit enters a regenerating cycle. First, a backwash phase reverses water flow through the mineral tank to flush any dirt out of the tank. Then in the recharge phase, the concentrated sodium-rich salt solution from the brine tank is flushed through the mineral tank. When the very strong brine solution is flushed through the mineral tank that has beads already saturated with calcium and magnesium, the sheer volume of the sodium ions is enough to drive the calcium and magnesium ions off the beads. The sodium collects on the beads, replacing the calcium and magnesium, which go down the drain. Once this phase is over, the mineral tank is flushed of excess brine and the brine tank is refilled.
Does a water softener make water less saline?
No, water softeners exchanges sodium (or potassium) ions for calcium or magnesium ions, but the total measurement of TDS does not change. Therefore, water softeners only make hard water softer.