Going to hijack this comment to ask about something I've always wondered: how robust are "appropriate" drinking levels to the different things you can reasonably expect people to do with the water? Not all water is simply drunk as is.
For example, I like to make beans in my slow cooker. This involves simmering them for 9 or 10 hours, periodically adding more water. In theory, this will increase the concentration of fluoride because the fluoride doesn't boil off while the water does. I assume, based on how much water I need to keep adding, this could double the fluoride concentration. Is that still appropriate levels? What about a cup that has been left out such that a lot of the water evaporates? That won't increase the amount of fluoride, but will increase its concentration.
I have to assume the "wiggle room" they build into the fluoridation rate handles these cases, but it's been hard to find any details on it since most of the results are about stuff like boiling water removing fluoride or turning it into poison fluorine gas and stuff.
Nevertheless, every time I see discussion where people talk about safe levels, I wonder how that works with all the things people do with water other than just drinking it as is.