Some water systems with naturally occurring fluoride must treat their water supply to remove the excess fluoride to comply with the Safe Drinking Water Act limits. Children under nine years of age exposed to levels of fluoride greater than about two mg/L may develop a condition known as mottling or discoloration of the permanent teeth. In certain cases the teeth become chalky white in appearance. The U.S. Environmental Protection Agency has advised a secondary maximum contaminant level (SMCL) limit of two mg/L to protect against this aesthetic or cosmetic adversity from fluorides in drinking water. Further, federal regulations require that fluoride not exceed a concentration of four mg/L in drinking water. This is an enforceable maximum contaminant level (MCL) standard; it has been established to protect public health.

Exposure to drinking water levels above four mg/L for many years may result in cases of crippling skeletal fluorosis, which is a serious bone disorder resembling osteopetrosis and characterized by extreme density and hardness and abnormal fragility of the bones (sometimes called .marble bones..) When a community water system exceeds the MCL of four mg/L, it must notify each of its customers by issuing a public notice to those customers. This notice outlines the limitations and health effects from high fluoride levels in drinking water and points out home treatment systems and bottled water as possible drinking water source alternatives.