Deionized Water:
Ion free water is known as Deionized or Demineralised water. Hard water is easily softened or rather deionized by synthetic ion-exchange resins. By deionized water is meant water contains no dissolved electrolyte, no cations and anions except H+ and OH– ions.
Distilled Water:
The only other process for the removal of all the ions in water is distillation. Distilled water is purer than deionized water. It may contain SiO2 and CO2.