Do you have more information on this? I thought that fluoride was toxic and thus shouldn't be swallowed. Are the quantities too small to harm you yet sufficient to prevent the formation of caries?
Water fluoridation rates are well under dangerous levels - about 0.7 mg/L for artificially fluoridated water, vs 2+ mg/L long-term to actually cause any problems. Even that small amount helps with reducing tooth decay, as was shown in the US in studies starting in the 50s comparing areas with naturally fluoridated water with areas without it.
