What is Deionized Water?

What is deionized water? Read on to find out.

If you need to remove ionic dissolved salts and minerals from water, you will need a process called deionization.


What is deionized water? To begin, you need to learn about deionization. Deionization is one of the most efficient processes known for removing ionic dissolved salts and minerals from water. The deionization process uses synthetic ion exchange resin to remove dissolved solids from water by ion attraction and exchange. This synthetic resin is charged with either hydrogen or hydroxide ions which causes the resin to release their ions in an exchange for the positively charged cations which may be present in the raw feed water supply.

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Two Types of Deionizers

Two types of deionizers are commonly used, mixed-bed and separate bed. A mixed-bed deionizer combines both cation and anion resins in a single vessel. Mixed-bed deionizers can produce very high water quality that approaches the theoretical limits of purity and a neutral pH of 7.0. A separate bed system consists of separate vessels of cation and anion resin. Separate bed deionizers have the economical advantage of 16-40% greater exchange capacity than an equivalent amount of mixed-bed resin. However, the water produced by separated bed deionizers is lower in quality than by mixed-bed deionizers and may require the use of a mixed-bed polisher if higher quality water or a neutral pH is needed.

Service Exchange Deionization?

Service exchange deionization uses this ion exchange resin in movable tanks or cylinders. These tanks are typically lined, fiberglass pressure vessels of varying sizes. Each size will accommodate specific total production capacities and flow rates to fit various situations precisely. Service deionization is a clean and simple way to produce purified water. All of the equipment, regeneration, maintenance and repair is provided by the service company. The deionizers are installed on your tap water and operate on line pressure to provide ionic containment removal. Eventually the ability of the deionizers to remove ionic impurities becomes “exhausted” and the service exchange company sends a service-person to remove the tanks on site and replace them with freshly regenerated units.


When most of the available hydrogen and hydroxide ions attached to the ion exchange resin during the initial regeneration cycle have been exchanged for ionic impurities in the water, the resin tank is “exhausted” and requires replacement. The exhausted deionizer is brought back to the service facility for regeneration.

During regeneration, an acid solution is drawn through the cation resin and a caustic solution is drawn through the anion resin. The cations and anions previously removed from the water supply are released by the resin in exchange for hydrogen and hydroxide ions present in high concentrations in the regeneration solution. A proper regeneration process is critical. Improper regeneration will result in reduced deionizer exchange capacity, lower total volume output and lower water quality.

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