One question I had was whether fluoridated water provides additional benefit if you are already using a fluoridated toothpaste. Obviously, having it in the water would benefit people who don't regularly brush their teeth, but it's not obvious that it's helpful if you already are getting your fluorine from the toothpaste. It's of interest to me because I drink non-fluoridated well water, but brush my teeth daily with a modern toothpaste. Anyone know?

My quick attempt to research this lead me to this nice Nature article from last year: https://www.nature.com/articles/d41586-021-02924-6. The article helps to quantify the positives of fluoridation of water: real, but not as large as one might guess. The bulk of the article is about someone who sued the EPA to prevent fluoridation of public water supplies. From what I can tell the suit is much delayed but still in progress: https://fluoridealert.org/issues/tsca-fluoride-trial/.