Deionized water (DI water) is a highly purified form of water from which nearly all dissolved mineral ions have been physically removed. This purification is necessary in scientific and industrial settings where trace amounts of charged particles could interfere with sensitive processes or equipment. The resulting product has extremely low electrical conductivity, making it suitable for applications requiring high purity and minimal interference.
Understanding the “Ions”
Ions are atoms or molecules that carry a net electrical charge because they have either gained or lost electrons. Positively charged ions are known as cations, while negatively charged ions are called anions. Common examples of cations found in untreated water include calcium, magnesium, and sodium, while anions include chloride, sulfate, and nitrate.
These charged particles are the primary target of deionization because they elevate the water’s electrical conductivity. In applications like electronics manufacturing or laboratory analysis, high conductivity can cause short circuits or skew experimental results. The goal of deionization is to exchange these unwanted ions for the components of a pure water molecule, ensuring the water acts as a non-conductive, neutral solvent.
The Process of Deionization
The creation of deionized water relies on a specialized technique called ion exchange, which uses synthetic resin beads. Water is passed through two types of resin beds: a cation exchange resin and an anion exchange resin. The cation resin is loaded with hydrogen ions (H+) and is designed to attract and swap positively charged ions from the water with its own H+ ions.
Next, the water flows through the anion resin, which is charged with hydroxide ions (OH-). This resin attracts and exchanges the negatively charged ions in the water for OH- ions. The hydrogen ions released by the cation resin and the hydroxide ions released by the anion resin then combine chemically. This combination forms a new, pure water molecule (H2O), effectively replacing the mineral ions.
For applications requiring the highest level of purity, a mixed-bed deionization system is often used. This approach combines both cation and anion resins within a single tank, maximizing contact between the resins and the water. This mixed arrangement ensures a more complete removal of trace ions, achieving exceptionally low conductivity.
Deionized vs. Distilled Water
Deionized water and distilled water are both purified, but their purification methods and resulting contaminant profiles are fundamentally different. Deionization is a chemical process that specifically targets and removes ionic impurities using ion exchange resins. It is highly effective at achieving extremely low levels of total dissolved solids (TDS) and very low electrical conductivity.
Distillation, conversely, is a thermal separation process where water is boiled into steam and then condensed back into a liquid. This method leaves behind non-volatile contaminants, including mineral salts, heavy metals, and most microorganisms. While distillation removes most ionic compounds, it also removes a wider range of non-ionic substances.
A key distinction is that deionization does not reliably remove non-ionic contaminants, such as bacteria, viruses, or certain organic compounds. Distillation, due to the boiling and condensation steps, is generally more effective at removing these biological and volatile organic impurities. Therefore, the choice depends on the specific application: DI water is preferred where minimal electrical conductivity is paramount, while distilled water is favored when the removal of biological contaminants is the main concern.
Common Applications and Consumption Safety
Common Applications
Deionized water is the standard for purity across a wide range of sensitive industries. It is routinely used in laboratories for preparing chemical solutions and cleaning glassware where mineral residue would compromise results. The electronics industry relies on DI water for rinsing semiconductor wafers, as its non-conductive nature prevents damage to microcircuitry. Industries also utilize DI water in cooling systems and high-pressure boilers to prevent mineral scale buildup and corrosion inside machinery.
Consumption Safety
While deionized water is technically safe to drink, it is not recommended for regular consumption. The purification process removes beneficial minerals like calcium and magnesium, which the human body needs. The lack of ions makes DI water highly reactive, meaning it will actively attempt to leach minerals from anything it contacts, including the body’s tissues and tooth enamel. Additionally, the deionization process does not remove non-ionic pathogens like bacteria or viruses, meaning DI water is not necessarily sterile. Purified water for drinking is typically filtered via methods that retain beneficial minerals or include sterilization steps.