Deionizers can be categorized as mixed bed systems or dual bed systems. Mixed bed systems contain both cation and anion resins inside a single vessel, and dual bed systems contain different resin types separated in different vessels.
Dual bed deionizers typically produce water of poor quality, which is generally unacceptable for medical purposes, such as in hemodialysis, according to Aqua Technology. As a result, dual bed deionizers are often used as a pretreatment for mixed bed deionizing systems. In such a configuration, the mixed bed system polishes the water to a higher ionic quality. Both of these deionizers may either be portable or permanent exchange.