Health Secretary Robert F. Kennedy Jr. kicked off a tour through southwestern states on Monday by calling on states to ban fluoride in drinking water supplies, a move that would reverse what some medical experts consider one of the most important public health practices in the country’s history.

The announcement came at a news conference in Utah, the first state to enact such a ban into law. The state’s new law is set to take effect in early May, despite concerns from public health experts who consider fluoridation of water core to preventing tooth decay.

“It makes no sense to have it in our water supply,” Mr. Kennedy said, echoing a position he took during the 2024 presidential campaign. “I’m very, very proud of this state for being the first state to ban it, and I hope many more will come.”

The Centers for Disease Control and Prevention, which Mr. Kennedy oversees as health secretary, has listed fluoridation as one of the 10 great public health achievements of the 20th century. After the news conference, Stefanie Spear, Mr. Kennedy’s principal deputy chief of staff, said Mr. Kennedy would direct the C.D.C.’s community preventative services task force to study fluoride and make a new recommendation.

Mr. Kennedy appeared at the news conference alongside the administrator of the Environmental Protection Agency, Lee Zeldin, who announced that the E.P.A. would re-examine research on potential health risks of fluoride in water.

The current standard “was most recently reviewed July of 2024, but a lot has happened since July of 2024,” Mr. Zeldin said. The review of safety data “wouldn’t be happening, if not for Secretary Kennedy,” he added.