In distillation, water is boiled to produce water vapor. When water reaches its boiling point, bacteria are killed and steam is created. A cooled surface condenses the steam into liquid water. The solutes and other contaminants remain in the boiling solution and are not vaporized. Distillation will be able to separate bacteria, viruses, cysts, heavy metals and inorganics from water. However, distilled water is not completely purified. Steam may carry some contaminants with almost similar boiling points. Distilled water may still contain small amounts of dissolved solids, dissolved gases and volatile components. It contains no salts and nutrients. 99.9% pure water is obtained from distillation.
In the preparation of deionized water, ions are removed using ion exchange chromatography. Calcium, magnesium and other heavy metal ions are removed from the water as it is passed through a resin column containing charged synthetic resin beads or granules. The resin column has specific ionic binding sites which can attract the ions in water. Due to the resin's greater affinity for other ions, cations and anions are exchanged for hydrogen and hydroxyl ions respectively. This process also removes non-ionic gases. Deionized water does not contain ions and has a low conductivity. It is more purified than distilled water. Ion exchange chromatography is quicker than distillation and has a greater percent recovery. Deionized water has become an important factor in medical, laboratory, pharmaceutical, cosmetics, electronics manufacturing, food processing, plating and industrial processes.
In osmosis, water and the concentration gradient occurs across a semi-permeable membrane. Water will dilute the contaminants. The process of osmosis can be slowed, stopped or reversed with the addition of pressure. In reverse osmosis, water will be made to move against the concentration gradient. Water is separated from other elements as it is passed through a plastic chamber with a semi-permeable membrane under pressure.