Fluoridation is the addition of the chemical fluoride in drinking water to reduce tooth decay. Since fluoridation treatment became common practice over 50 years ago, tooth decay has been reduced 40 to 65 percent. This manual provides data and guidance on the design, operation, and maintenance of fluoridation systems in water treatment. Coverage includes human health effects of fluoride, calculating dosage, feed systems, installation, operation, maintenance, and defluoridation.