Centers for Disease Control.
For 12 hours, excess hydrofluorosilicic acid was diverted to a 127-home community water supply. Fluoride levels peaked at 51 parts per million (ppm). Water acidification caused copper to leach from the domestic plumbing; raising copper levels to 25-41 ppm. Fifty-two (33 per cent) of those who drank hyperfluoridated water developed mild gastroenteritis. Vomiting was uncommon and symptom onsets usually occurred greater than 30 minutes after drinking water; suggesting that fluoride, rather than copper, caused illness. Skin contact with hyperfluoridated water caused itching and skin rashes.