HHS’ proposed recommendation of 0.7 milligrams of fluoride per liter of water replaces the current recommended range of 0.7 to 1.2 milligrams. This updated recommendation is based on recent EPA and HHS scientific assessments to balance the benefits of preventing tooth decay while limiting any unwanted health effects.

As AP notes:

A scientific report five years ago said that people who consume a lifetime of too much fluoride — an amount over EPA’s limit of 4 milligrams — can lead to crippling bone abnormalities and brittleness. That and other research issued Friday by the EPA about health effects of fluoride are sure to re-energize groups that still oppose adding it to water supplies.