What is the content of fluoride concentration in water that's considered safe for the prevention of dental decay?

Water : Municipal water supply keeps Fluoride comcentration at between .7 and 1, 0 ppm.

Water supply fails: Major dental researchers concede that fluoride’s benefits are topical not systemic (fejerskov 1981; carlos 1983; cdc 1999, 2001; limeback 1999; locker 1999; featherstone 2000). Children in non-fluoridated communities are already getting the so-called “optimal” doses from other sources (heller et al, 1997).

0.8 part per million: Fluoride is incorporated into the crowns of permanent teeth as they calcify, changing hydroxyapetite crystals to fluorapetinte crystals which are more resistant to acidic damage. The crowns of permanent teeth (excluding wisdom teeth) form from about 6 months in utero to age 8, during which time ingested Fluoride is important. See your dentist for proper ingested/topical Fluoride balance.

Optimum is 0.7 mg/l: The World Health Organization considers 1.5 mg/l of fluoride or lower safe In drinking water. Above 1.5 mg/l dental fluorosis may occur to an objectionable degree. Concentrations between 3-6 mg/l may cause skeletal fluorosis. Above 10 mg/l can cause crippling skeletal fluorosis. Optimally fluoridated water in the USA is kept at about 0.7 mg/l and is not a problem.