Demineralization is a type of water purification. While it can refer to any treatment process that removes minerals from water, the term demineralization is typically reserved specifically for ion exchange (IX) processes used for near total removal of ionic mineral contaminants. Often, the terms demineralization and deionization are used interchangeably. IX demineralization utilizes both cation and anion exchange resins, sometimes even in the same column or bed. Following demineralization, the treated water will be of a high level of purity comparable to distilled water, but typically at a much lower cost.

In the presence of water, minerals and salts dissociate into their constituent ions. These dissolved solids consist of negatively-charged ions known as anions, and positively-charged ions known as cations, each of which are attracted to counterions (or ions of an opposing charge). Present within an IX column is a resin which consists of plastic beads to which an ionic functional group has been bound.

hese functional groups loosely hold ions of an opposing charge through mutual electrostatic attraction. During an active IX cycle, a water with dissolved ions is introduced to the resin. The ions in solution will exchange places with the ions on the resin beads, clinging to the resins functional groups even as the resulting solution is drained away. IX happens when one ion has greater affinity for the functional group than the ion that is already present. The specific ionic contaminants present will dictate whether anionic and/or cationic resin types are needed.