I see this all the time, albeit usually from the conspiracy theory nutjobs, that water shouldn't be fluoridated and that it's "poison." Obviously if you ingest large amounts of it (oh, you know, just like literally anything I can think of) it can be poisonous, but those concentrations aren't found in our water systems to my knowledge. I've read plenty of research displaying its effectiveness in preventing dental caries, but haven't seen much addressing health concerns. What evidence is there of adverse effects as a result of controlled water fluoridation other than mild dental fluorosis? I'm doubting there's too much supporting evidence seeing as the people making these claims can't even provide the research themselves (what else is new, lol).