Both reverse osmosis (RO) and de-ionization (DI) are techniques to purify water. Reverse osmosis relies on forcing water through a semi-permeable membrane to filter out impurities and is commonly used in desalinization and the production of drinking water. De-ionization is a chemical process that removes most chemical ions from water. Both techniques are commonly used in commercial and industrial applications as a way to remove contaminants that may interfere with processes, or leave residues upon evaporation. They are particularly common in the semiconductor, food/beverage, and pharmaceutical industries which need large amounts of very pure water.