The optimal fluoride level recommended by the U.S. Public Health Service and CDC (Centers for Disease Control) for drinking water is 0.7 parts per million (ppm).
Information on the fluoride status of community water supplies, listed by state, county and city can be accessed on the CDC website at: http://apps.nccd.cdc.gov/MWF/Index.asp
Further information on community water fluoridation can be assessed at: American Dental Association: http://www.ada.org/en/public-programs/advocating-for-the-public/fluoride-and-fluoridation