What must be done once the resin in the ion-exchange softening process can no longer soften water?

In the ion-exchange softening process, the resin is responsible for exchanging calcium and magnesium ions in the water with sodium ions. Over time, the resin becomes saturated with these hardness ions and can no longer effectively soften the water.

The correct approach when the resin reaches this saturation point is to regenerate it. This process involves flushing the resin with a concentrated salt solution (typically sodium chloride), which allows the sodium ions to displace the accumulated calcium and magnesium ions from the resin beads. This regeneration restores the resin's ability to soften water, enabling the system to continue functioning efficiently.

Disposing of the resin or replacing it entirely would be more costly and unnecessary, as regeneration is a standard practice that extends the life of the resin. Rewashing is not a recognized term within this context; the proper terminology is regeneration.