Deionized water: As the name implies, all ions except hydrogen ions and hydroxyl ions in water are removed from water, which is produced by the dissolution and ionization of electrolytes in water. That is, the electrolyte dissolved in water is removed. Because ions produced by the ionization of electrolytes dissolved in water can increase the conductivity of water, the purity of deionized water is naturally measured by conductivity. Deionized water is basically prepared by ion exchange method. However, deionized water may contain a non-electrolyte that cannot be ionized, such as ethanol.
Pure water: Pure water is to remove all electrolytes and non-electrolytes, and it can also be said that all non-aqueous substances in water are removed. It's basically made of reverse osmosis. Because most of the non-electrolyte in reverse osmosis pretreatment is removed by activated carbon, the conductivity is very easy to measure, so the purity of pure water is often measured by conductivity. However, in order to obtain high-purity pure water, it is still necessary to remove electrolytes by mixed bed and EDI.
Another way to improve the purity of water supply is distillation. The produced water is called distilled water, which mainly removes electrolytes and non-electrolytes whose boiling point is quite different from that of water. Non-electrolyte with boiling point equivalent to water cannot be removed, and the purity is also measured by conductivity.