What does deionise mean?
To deionise is to remove charged particles — ions — from a substance, most commonly water. Water that has been deionised passes through ion-exchange resins that strip out dissolved mineral salts such as calcium, sodium, and chloride, leaving it exceptionally pure. The result, known as deionised or demineralised water, is essential wherever even trace impurities matter: laboratories rely on it for chemical analysis, semiconductor factories use it to rinse microchips, and car owners add it to batteries and cooling systems to prevent mineral deposits. The term is the standard British spelling, with American English preferring 'deionize'. It belongs firmly to technical registers — chemistry, engineering, and manufacturing — and rarely appears in casual conversation. Its opposite is ionisation: where ionising adds charge, deionising removes it. For anyone working with sensitive equipment or chemical reactions, understanding what deionised means signals a level of purity that ordinary filtered or distilled talk simply doesn't capture with the same precision.
verbTo remove ions from a substance, especially water, typically by passing it through an ion-exchange resin.
- To remove dissolved ions from a liquid (especially water) using ion-exchange methods.
"The laboratory deionises all water used in its chemical analyses to ensure accurate results."
"The aquarium keeper deionises tap water before adding it to the tank."
"Semiconductor plants deionise water to parts-per-billion purity for rinsing silicon wafers."
That ultra-pure 'deionised water' in your lab or car battery is so hungry for ions it can actually taste metallic — because it strips minerals from anything it touches, including you.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does deionise come from?
The word deionise combines the Greek-derived prefix 'de-' (indicating removal) with 'ion', a term coined by Michael Faraday in 1834 at the suggestion of William Whewell, from the Greek 'ion' meaning 'going' — the neuter present participle of 'ienai', to go — because ions move toward electrodes. The '-ise' suffix reflects British verb-forming convention, giving the American variant 'deionize'. The term emerged in twentieth-century scientific usage as ion-exchange technology became widespread.
Related word forms
How deionise is actually used
This is chiefly the British spelling; American English uses 'deionize'. The word is technical and formal, appearing mostly in chemistry, laboratory, and industrial contexts rather than everyday speech.
Easily confused with deionise
Ionise means to convert an atom or molecule into an ion by adding or removing electrons, while deionise means the reverse process of removing dissolved ions from a substance such as water.