What is Ion Exchange?
Most common ion exchange systems use a Zeolite resin bed and simply replace unwanted ions (Ca 2+ and Mg 2+) with benign (soap friendly) sodium or potassium ions. This is the common Water Softener.
A more rigorous type of ion exchange swaps hydrogen (H+) ions for unwanted cations and hydroxide (OH-) ions for unwanted anions. The result is H+ + OH- - > H 2 O.
This system is recharged with hydrochloric acid and sodium hydroxide. The result is essentially Deionised Water.