The Collaborative International Dictionary
deionizer \de*i"on*iz`er\ n. (Chem.) an apparatus used to remove ions from a solution; a common variant contains a mixture of cation exchange resin in the acid form and anion exchange resin in the hydroxyl form inside a replaceable cartridge; ions in aqueous solution are exchanged for the elements of water by passing the solution through the mixed resin.
Note: In chemistry and biochemistry, experiments often require water free from contaminating ions, and ordinary distilled water may be further purified by passing through a deionizer in order to render the ion content sufficiently low so as not to interfere with the investigation.
Usage examples of "deionizer".
I explained my conceit, keeping the upstairs part of the house turn-of-another-century except for a few sensible improvements: media center, smoke and particulate detectors, a deionizer built into a squat wooden 1920s icebox.