Fluoride is an inorganic, monatomic anion with the chemical formula F-. Fluoride ions come from the element fluorine and can be found naturally in soil, rocks and water. Although, fluoride is present in most rainwater, fresh and saltwater sources, the concentration is low, at around 0.3 mg/L. In addition to this naturally occurring calcium fluoride, a synthetic, industrial version of fluoride is often added to tap water in the form of sodium fluoride, fluorosilicic acid and sodium fluorosilicate.
