What does deionised mean?
Deionised is an adjective describing water, solutions, or other materials from which dissolved ions have been removed. The process is usually carried out with ion-exchange resins, which replace charged particles with hydrogen or hydroxide ions, and is common in laboratories, electronics, pharmaceuticals, and boiler systems. The word is especially frequent in the phrase “deionised water,” where it indicates a reduced level of mineral contaminants such as calcium, magnesium, chloride, and sulfate ions. It is distinct from distilled water, which is purified through vaporisation and condensation, and from demineralised water, a broader term concerning the removal of mineral substances. Although deionisation makes water suitable for many sensitive technical applications, it does not guarantee sterility or complete chemical purity. The British spelling “deionised” and the American variant “deionized” refer to the same treatment.
adjectiveHaving had dissolved ions removed, especially by passing water or another solution through ion-exchange materials. The term is most commonly used for water and laboratory solutions.
- Having undergone deionisation, especially through the removal of dissolved ions by ion exchange.
"The laboratory uses deionised water to minimise interference from dissolved mineral ions."
"The technician rinsed the electrodes with deionised water before testing them."
"A deionised solution was used to prevent mineral ions from affecting the results."
Deionised water is laboratory-clean, not necessarily laboratory-pure: it can still absorb carbon dioxide and other contaminants from the air.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does deionised come from?
Deionised was formed in English by combining the prefix de-, meaning removal or reversal, with ion and the verbal suffix -ise. The underlying noun ion comes from Greek ion, meaning “going” or “traveller,” a term associated with electrically charged particles. The -ised spelling is characteristic of British English, while the corresponding American form is commonly spelled deionized.
Related word forms
How deionised is actually used
This is chiefly a technical and laboratory term, especially associated with water and aqueous solutions. British English usually uses the spelling “deionised,” while American English more commonly uses “deionized.” Deionised does not necessarily mean sterile, safe to drink, or completely free of every possible contaminant.
Easily confused with deionised
Deionised describes material from which dissolved ions have been removed, whereas demineralised describes material from which mineral salts or other inorganic substances have been removed.
Deionised water is typically purified by ion exchange, while distilled water is purified by vaporisation and condensation.