Definition of Demineralised, Distilled and Deionised Water

Demineralised water is pure water that has minerals removed and is usually obtained through distillation or deionisation.


Distilled water is obtained through the process of evaporation and condensation. Water is heated to boiling point, changing it to steam and leaving impurities behind.

As the steam cools, it condenses back to water. This condensate is collected as distilled water.

The heating process kills bacteria and viruses which makes the water drinkable.

It also removes virtually all organic and inorganic contaminants and produces a water that is consistently pure as it is not dependent on the quality of filters, resin or membrane.

Deionised water is obtained through the use ion-exchange resins. These resins exchange hydrogen ion and hydroxide ion for dissolved minerals, which then recombine to form water.

The process involves the removal of mineral ions such as cations like sodium, calcium, iron and copper, and anions like chloride and sulphate. However, deionisation does not significantly remove uncharged organic molecules or bacteria.

It is a cheaper way of producing pure water but could not produce water with the same purity and consistency of distillation.

Distilled water could be used for applications requiring demineralised water but not necessarily the other way round.