Ion exchange removes unwanted ions from a raw water by transferring them to a solid material, called an ion exchanger, which accepts them while giving back an equivalent number of a desirable species stored on the ion exchanger skeleton. 
         The ion exchanger has a limited capacity for storage of ions on its skeleton, called its exchange capacity; because of this, the ion exchanger eventually becomes depleted of its desirable ions and saturated with unwanted ions. It is then washed with a strong regenerating solution containing the desirable species of ions, and these then replace the accumulated undesirable ions, returning the exchange material to a usable condition.This operation is a cyclic chemical process, and the complete cycle usually includes back washing, regeneration, rinsing, and service.