The Collaborative International Dictionary of English v.0.48:

fluoridization \fluoridization\ n.
   the addition of a fluoride to the water supply (to prevent
   dental decay).

   Syn: fluoridation.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

fluoridization
    n 1: the addition of a fluoride to the water supply (to prevent
         dental decay) [syn: fluoridation, fluoridization,
         fluoridisation]