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.
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.