Drinking fluoridated water may ruin your baby’s smile.

That’s the latest warning handed down by the Environmental Working Group, a public interest and environmental watchdog whose research about the toxicity of Teflon got DuPont to agree to change the popular coating’s chemistry.

EWG’s current campaign centers on the youngest of 18million customers of the Metropolitan Water District of Southern California. And it’s timely because come July, the district will begin fluoridating the area’s 1.7billion gallon daily water supply.

The group’s concern?

Parents may not know that giving fluoridated water to infants younger than 1 has the potential to cause enamel fluorosis in the child’s permanent teeth still in development in the gums.

In its defense, the MWD says fluoride occurs naturally in tap water, and drinking water with the right amount of fluoride has been shown to reduce tooth decay.

But the Environmental Working Group isn’t the only group raising questions.

Babies already consume “more than the optimal amount of fluoride” for their size through formula or food prepared with fluoridated water, according to the American Dental Association.

According to the Centers for Disease Control and Prevention, about 30percent of children have enamel fluorosis, a condition that ranges from barely noticeable white flecks to substantial corrosion of the enamel on teeth.

To reduce the risk of fluorosis, the ADA recommends mixing powdered infant formula with low-fluoride or fluoride-free bottled water labeled as “purified,” “demineralized,” “deionized” or “distilled.”

Filtering water through reverse osmosis also does the trick in reducing fluoride over-consumption.

“What parents need to know is the concerns about fluoride have gone mainstream,” says Richard Wiles, co-founder and executive director of the EWG. “The ADA, the leading authority on dental health, has concerns about fluoridated water.”

And enamel fluorosis isn’t the only health concern associated with the overconsumption of fluoride.

In March 2006, the National Academy of Sciences identified fluoride as a potent hormone mimic that may affect normal thyroid function. And a 2006 peer-reviewed study by four Harvard scientists and doctors supports ongoing concerns that fluoridated water is linked to osteosarcoma, an often fatal form of bone cancer in boys.

“It’s a potent substance,” Wiles says. “It’s not to be taken lightly.”

To find out how much fluoride your tap water contains, call your utility company for its latest water-quality report.