Fluoride is added to drinking water across the U.S., but residents of some states are considerably more likely to be drinking fluoridated water than others, according to data from the U.S. Centers for Disease Control and Prevention ( CDC)

Robert F. Kennedy Jr.'s recent comments on fluoride are prompting questions about its safety in drinking water. Here's what to know.

The CDC calls the practice of adding fluoride to tap water systems one of the 10 greatest public health achievements of the last century.

President-elect Donald Trump announced Thursday that he planned to nominate Robert F. Kennedy Jr. to lead the Department of Health and Human Services.

For years, local water authorities have considered the addition of low concentrations of fluoride to drinking water a public health achievement. The Centers for Disease Control and Prevention recommends it, citing evidence showing that fluoride prevents cavities in children — the No. 1 chronic disease in kids.

Kennedy Jr. has previously said that if Republican President-elect Donald Trump won the White House, the administration would advise water systems in the United States to remove fluoride. This is despite experts and officials saying the mineral is both safe and beneficial to people’s dental health.

The Centers for Disease Control call the addition of fluoride in water one of the biggest medical advances in the 20th century, noting that it led to healthier teeth.