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
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. The membrane allows fluid to pass through but blocks contaminants like bacteria, ions and chemicals. A high pressure pump on the impure water side provides the driving force that is greater than the normal osmotic pressure of the two solutions. It forces the water against its natural direction. Reverse osmosis separates water from bacteria, salts, sugars, proteins, particles, dyes and other contaminants. It removes harmful chemicals like hexavalent chromium, radium 226/228
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