Fluoride is put in water supply in order to reduce the occurrence of dental related health issues like tooth decay or bacterial growth in the mouth.

Fluoride is a compound of fluorine which is a naturally occurring element found in ground water and mineral rocks. When put into water supplies, it helps prevent tooth decay and is so effective in doing this that the Centers for Disease Control and Prevention named it one of 10 great public health achievements of the 20th century.

Taking into account the huge amount of time that is spent on tooth related treatments yearly in the United States(51-161million school/work hours), fluoridation of water is a healthy and cost effective means of reducing these numbers, and according to the American Dental Association, the life time cost of fluoridizing your water is less than the cost of one dental filling.

Basically, the idea behind putting fluoride in water is to prevent and reduce the occurrence of tooth decay in both children and adults.