Optimally the level of fluoride would be 0.7 to 1.2mg of fluoride per liter of water. Tables of optimal levels are dependent on the daily air temperature, see table 1. Due to the fact that people tend to drink more in warm weather, warmer weather dosage levels are much lower than those of colder weather. Dosages above this level have been know to cause cases of skeletal fluorosis. Skeletal fluorosis is the weakening of bones due to high levels of fluoride being deposited in them.
Dental fluorosis is characterized by a graying of teeth.
In severe cases, the tooth enamel begins to pit.