As of 1989, fluoridation in the U.S. was being practiced in at least 8000 communities serving more than 126 million people. An additional 9 million residents of over 1800 additional communities were consuming water that contained at least 0.7-mg/L fluoride from natural sources. Key facts about fluoride include:
• Briefly, fluoride is seldom found in appreciable quantities in surface waters and appears in groundwater in only a few geographical regions
• Fluoride is sometimes found in a few types of igneous or sedimentary rocks • Fluoride is toxic to humans in large quantities; it is also toxic to some animals • Based on human experience, small concentrations of fluoride (about 1.0 mg/L in drinking
water) can be beneficial
Theoretically, any compound that forms fluoride ions in water solution can be used for adjusting the fluoride content of a water supply; however, several practical considerations are involved in the selection of compounds:
• Cation to which the fluoride ion is attached must not have any undesirable characteristics. • Material should be relatively inexpensive and readily available in grades of size and
purity suitable for its intended use.