What does deionisation mean?
Deionisation is the removal of dissolved ions from a substance, most often water, using ion-exchange resins or comparable ion-exchange equipment. Ions are electrically charged atoms or groups of atoms, and their presence can affect conductivity, corrosion, laboratory reactions, and industrial processes. Deionised water is therefore used where very low ionic contamination is important, including electronics, pharmaceuticals, laboratories, and steam boilers. The term is not synonymous with every kind of purification: deionisation specifically concerns ions and does not by itself remove all organic chemicals, microorganisms, or gases, nor does it make water sterile. It also differs from complete demineralisation, which generally describes the broader removal of dissolved mineral material. Deionisation is a formal, technical noun, usually uncountable in scientific writing, although it can take a plural when referring to separate treatment installations. British English uses the -isation spelling, while US English commonly writes deionization.
nounThe process of removing dissolved ions from a substance, especially water, usually by passing it through ion-exchange resin. The resulting water is called deionised water.
- The removal of dissolved ions from a substance, especially water, typically through ion-exchange treatment.
"The laboratory uses deionisation to prepare water for trace-element analysis."
"The laboratory uses deionisation to prepare water for trace-element analysis."
"The treatment plant combines filtration with deionisation before the water enters the high-pressure boilers."
Uncommon; the noun is normally used in the singular or as an uncountable mass noun.
"The pilot plant's two deionisations supply separate laboratories."
Ion-exchange resin swaps unwanted ions for hydrogen and hydroxide ions, leaving water ultrapure rather than sterile.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does deionisation come from?
Deionisation is an English formation combining the prefix de-, meaning removal or reversal, with ionisation. The element ion comes from the Greek iōn, a participle meaning “going,” and was introduced into chemistry in the 19th century in connection with the movement of charged particles during electrolysis. Deionisation developed alongside ion-exchange technology and became established in technical language, particularly in water treatment and laboratory practice.
Related word forms
How deionisation is actually used
This is a formal technical term and is usually treated as an uncountable noun. British English uses the -isation spelling, while US English commonly writes deionization.
Easily confused with deionisation
Demineralisation refers more broadly to removing dissolved mineral substances, whereas deionisation specifically describes the removal of ions.