Pure water, also known as purified water, is water from a source that has removed all impurities. Distilled water is the most common form of pure water. Water, H2O, is a pure substance, a compound made of hydrogen and oxygen. Although water is the most abundant substance on earth, it is rarely found naturally in its pure form. Most of the time, pure water has to be created. Pure water is called distilled water or deionized water
Parameters of water purity
inorganic ions (typically monitored as electrical conductivity or resistivity or specific tests)
organic compounds (typically monitored as TOC or by specific tests)
bacteria (monitored by total viable counts or epifluorescence)
endotoxins and nucleases (monitored by LAL or specific enzyme tests)
particulates (typically controlled by filtration)
gases (typically managed by degassing when required)