The federal government lowered its recommended limit on the amount of fluoride in drinking water for the first time in nearly 50 years, saying that spots on some children's teeth show they are getting too much of the mineral.

Fluoride has been added to U.S. water supplies since 1945 to prevent tooth decay. Since 1962, the government has recommended adding a range of 0.7 milligrams to 1.2 milligrams per liter.

But...