Fluoride is added to drinking water in the form of:
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