Fluoride is added to drinking water in the form of:
High-Yield Explanation
Fluoride compounds used in water fluoridation
Fluorspar
Sodium fluoride
Silicofluoride
Sodium silicofluoride
Ammonium silicofluoride
Hydrofluosilicic acid.
Essentials of preventive and community dentistry
Soben Peter page no. 268