I suspect that as city councils look to cost-shifting to mitigate their considerable budget woes, they will become less concerned about the nebulous cost of cavities and more concerned with the demonstrable cost of chemicals, treatment plants, haz-mat disposal, and water plant maintenance workers and their pensions.
http://www.newmediaexplorer.org/chris/Clinch_2010_Costs_Artificial_Water_Fluoridation.pdf