Fluoride is a mineral found underground.
Tony McGrath with the Negaunee/Ishpeming Water Authority says the groundwater treated at water plants already contains an amount of fluoride in it.
"The concentration in our well water is .12 parts per million. What we do here is add enough extra fluoride from drones that we receive from a chemical company to bring that concentration up close to one part per million of fluoride," said McGrath.
It's included in tap water to strengthen kids' teeth, preventing any cavity growth.
Richard Forbes writes, "Fluoride is poison. It doesn't need to be in our drinking water."
Sherri Laitinen writes, "Anything is toxic if you have too much, including water! The trace amount added to water is one part per million! Definitely a good thing to help counteract our country's sugar-saturated diet!"
The only concern with too much fluoride is tooth spotting, but Dentist Brett Goymerac says that's a slim chance.
"The topical fluoride, whether it's in water, mouthwash, or toothpaste, can help reintroduce the minerals that are being broken down to help strengthen the teeth, hopefully preventing any dental work done to fix it," said Goymerac.
The U.S. Department of Human Health Services is trying to lower the dosage amount put in tap water.