The movement to stop fluoridating water has gained traction, in large part, because the government has recently cautioned the public about excessive fluoride. A report released late last year by the Centers for Disease Control and Prevention linked fluoride to an increase among children in dental fluorosis, which causes white or yellow spots on teeth. About 40 percent of children ages 12 to 15 had dental fluorosis, mostly very mild or mild cases, from 1999 to 2004. That percentage was 22.6 in a 1986-87 study.

Fluorosis is mostly a cosmetic problem that can sometimes be bleached away. But critics argue that spotted teeth are a warning that other bones in the body may be absorbing too much fluoride. Excessive fluoride can lead to increases in bone fractures in adults as well as pain and tenderness.

“Teeth are the window to the bones,” said Paul Connett, a retired professor of environmental chemistry and the director of the Fluoride Action Network, which advocates an end to fluoridated water.

Experts say that one possible factor in this increase may be that fluoridated water is consumed in vegetables and fruit, and juice and other beverages as well as tap water. And the consumption of beverages continues to increase.

In January, the federal Department of Health and Human Services recommended reducing the fluoride put into the water supply to 0.7 milligrams per liter of water. The longtime standard had ranged from 0.7 to 1.2 milligrams per liter. At the lowest level, the risk of fluorosis is decreased, the government says.

The government also informed parents of infants who exclusively use infant formula reconstituted with fluoridated water that their children face an increased risk of fluorosis and suggested they use low-fluoride water, like distilled water, some of the time. “It was a trigger,” said Mr. Connett. “People who had heard there is nothing wrong with fluoridation all of the sudden are hearing that kids are getting too much fluoride.”

Money worries and a growing distrust of government have also helped invigorate the movement. With the recession squeezing budgets and the cost of fluoride increasing (some fluoride is imported), communities have been more willing to take a look at the issue.