Days before the election, Kennedy posted on social media that a Trump White House would advise all U.S. water systems to remove fluoride from the public water supply, which goes against public health recommendations yet jibes with a large number of people who question the safety of fluoridating water.

Fluoride helps prevent tooth decay. It occurs naturally in some foods—tea, potatoes and shrimp, for example—and in some water. In 1945 Grand Rapids, in Michigan, became the first American city to add it to its drinking water. Today more than two-thirds of Americans have water with added fluoride piped into their homes.

Fluoride is missing from 43% of Californian faucets, including Bay Area towns of Los Altos, Santa Cruz, Novato and parts of Santa Clara, San Jose and Livermore.

Chicago residents expressed concerns about the future of vaccines and fluoride after President-elect Donald Trump tapped Robert F. Kennedy Jr., a controversial anti-vaccine activist to lead the nation's health agencies.