Most of the country’s population is served with water systems that have fluoridated water, but Robert F. Kennedy Jr., a key supporter of President-elect Donald Trump, has vowed to end that practice.

The debate over fluoride in drinking water isn’t new, but it has been elevated again with Kennedy’s push to remove the chemical, alleging it does more harm than good. However, proponents of fluoridated water have pushed back on the likely costly move to do so.