Fluoride has been added to our public water supplies since the 1950s. It was added because the Powers-That-Be assured us that it would lower cavity rates and cause no harm. After 70 years of adding fluoride to our water supplies, I can now state, with certainty that fluoridated water does not significantly reduce cavity rates and it is associated with serious health problems.
When you compare fluoridated with non-fluoridated countries, there is virtually no difference in cavity rates. Right now, the US is probably the most fluoridated country in the world. Most Western countries have looked at the science behind fluoridation and stopped using it. Nearly every other Western country has looked at the science behind water fluoridation and rightfully concluded that the harms of water fluoridation vastly outweigh the minimal purported benefits of less tooth decay. Israel was the last Western country to ban its use in tap water.