Water contains more than water
As we have seen before, the water contains small amounts of foreign substances:
- Solid, insoluble substances, such as sand or plant debris that you remove by filtration
- Soluble substances, that you do not see most of the time and that you can’t filter. These substances may be of inorganic or organic origin, they can be ionized (electrically charged) or not
In many cases, these soluble substances cause no problem. Drinking water containing some salinity is better for health than ultra-pure water. For some applications, however, these substances are considered as impurities and must be eliminated. Medical domain, nuclear and thermal power plants are very demanding of ionized water.
For the removal of ionized or ionizable foreign substances from water you can use the ion exchange process.
Deionized water, also known as demineralized water (DI water), is water that has had almost all of its cations and anions removed by ion exchange resin.
Deionization is a chemical process where cations are first exchanged toward Hydrogen ions (H+) on a cationic resin, followed by anion exchange toward Hydroxyl ions (OH-) on an anionic resin. Hydrogen and Hydroxyl ions then recombine to form H20 (pure water). Because most non-particulate water impurities are dissolved salts, deionization produces a high purity water that is generally similar to distilled water, and this process is quick and without scale build-up.
However, deionization does not significantly remove uncharged organic molecules, viruses or bacteria, except by incidental trapping in the resin. Specially made strong base anion resins can remove Gram-negative bacteria.