Health officials say some people are getting too much fluoride now because it is also added to toothpaste, mouthwash and other products.
Too much fluoride has become a common cause of splotches on teeth. One study found about 2 out of 5 adolescents have tooth streaking or spottiness from too much fluoride.
The government first began urging cities to add fluoride to drinking water in 1962.
Health officials credit fluoride in drinking water with reducing tooth decay by 25 percent over the course of a person’s lifetime. The Centers for Disease Control and Prevention (CDC) named community water fluoridation one of 10 great public health achievements of the 20th century.
The change announced Monday finalizes a proposal first made four years ago.