Deionized

Deionized water, also spelled deionised water, is water from which most or all dissolved ions have been removed. It is produced by passing water through ion-exchange resins that replace mineral ions such as calcium, magnesium, sodium, chloride, and sulfate with hydrogen and hydroxide ions, which combine to form pure water. A typical configuration uses a cation-exchange bed followed by an anion-exchange bed; mixed-bed polishing can achieve higher purity, and electrodeionization can provide regeneration-free operation. Deionized water is not the same as distilled water, though both yield very pure products; deionization specifically targets ionic impurities.

Key properties are extremely low ionic content and high resistivity, commonly measured by electrical conductivity. Because of this purity, deionized water is widely used for applications where mineral deposits or ionic contaminants must be minimized. It is commonly used for laboratory reagents, electronics wafer cleaning, pharmaceutical manufacturing, analytical instrumentation, and various cleaning and rinsing tasks.

Limitations and maintenance are important considerations. DI water can reabsorb carbon dioxide from air, forming carbonic acid and bicarbonate, which raises conductivity over time. It can also leach ions from containers and piping, and bacterial growth can occur if bioburden is present. Maintaining DI water systems requires resin regeneration with acid and base (or using electrodeionization), pretreatment to remove organics and particulates, and the use of compatible storage vessels to minimize contamination.