Whether governments and local authorities should add fluoride to tap water has always been a politically charged topic. In 1945, Grand Rapids, Michigan, became the first city in the world to take this step, in an effort to promote dental health.
"From epidemiological data, it was discovered that there was less decay in children's teeth in some areas versus others," Lucy O'Malley, an applied health scientist at the University of Manchester in the U.K., told Live Science. "They found this was because some areas had water supplies that had natural fluoride levels at around 1 ppm [part per million] and that was beneficial for protecting against caries," better known as cavities.
