The Ministry of Health recommends fluoride be added to the water at at concentration of between 0.7ppm to 1ppm, with a target of 0.85ppm. When fluoridation first started the target was 1ppm but the Ministry of Health reduced this to a range with a lower target sometime int he 1990s. Most councils that fluoridate target 0.85ppm but as a result of lobbying from FFNZ Auckland, Hamilton, Hastings and Kapiti Coast have reduced their target to 0.7ppm.
In 2016 the US Department of Health and Human Services reduced their range from 0.7ppm to 1.2ppm to a maximum target of 0.7ppm.
0.7ppm or more is typically higher than most drinking water in the world as most drinking water is sourced from rain, lakes or rivers.
Rain is typically very low, almost always below 0.1 ppm (unless it is in an area of heavy industrial F air pollution or volcanic gases). Surface water (lakes and rivers) are also very low in fluoride, only about 0.1 ppm or less. In some surface waters that are polluted by industry, the levels can be higher.
In a very few places some unusual geology has created lakes or rivers with high fluoride levels, into the tens or even hundreds of ppm. Hot Springs can also have high F levels.But almost nobody drinks these high fluoride waters.