In my youth I lived off a well and did not have access to fluoridated water. My parents still live in that house. There are large swaths of people who live off of a well in the United States. We started adding fluoride to water because our knowledge at the time said it was a good idea (and still probably is). The rates of tooth decay falls when fluoride is introduced in drinking water.

https://www.cdc.gov/fluoridation/pdf/natures_way.pdf

But the only places that have fluoride added to the water are metropolitan areas (at least around me in a Midwestern state).