In mixed-bed deionizers the cation exchange and anion-exchange resins are intimately mixed and contained in a single pressure vessel. The thorough mixture of cation-exchangers and anion-exchangers in a single column makes a mixed-bed deionizer equivalent to a lengthy series of two-bed plants. As a result, the water quality obtained from a mixed-bed deionizer is appreciably higher than that produced by a two-bed plant. 

The vessel can be in the form of a large stainless steel or reinforced fiberglass column containing many hundreds of liters of resin, or a small disposable/redeemable cartridge which, when exhausted, can either be thrown away or sent hack to the original supplier for regeneration.