We’ve been getting dosed with flouride for what, 40-50yrs? And who knows what else? IIRC, tests have shown traces of Xanax, Prosac, Valium, antibiotics etc etc etc in many municipal water supplies, from contaminated groundwaters. They can’t filter out everything introduced into the system.
Many chemicals are natural. We have high arsenic in the water here, but we live where almonds are grown.