How Does Fluoride Get Into Tap Water?
Naturally Occurring Fluoride
Fluoride is a mineral that can occur in drinking water naturally as a result of the geological composition of soils and bedrock. Very little natural fluoride is found in western Washington, but in eastern Washington it is fairly common.
Public water systems are required to test for fluoride as part of routine monitoring for inorganic chemicals (typically done every three years). If your water source contains naturally occurring fluoride at or above the Washington state reporting level of 0.2 mg/l, it will be shown in your water system's annual water quality report. If it is not shown in this report, this means that the level of naturally occurring fluoride is less than 0.2 mg/l (considered "not detected"). Nearly all of Washington Water–owned Group A water systems have non-detected levels of natural fluoride (a few are right at or slightly above 0.2 mg/l).
Fluoride can also be added to community drinking water supplies as a public health measure for preventing tooth decay and reducing cavities. The decision whether or not to add fluoride to drinking water is made at the state or local level. Washington state does not require public water systems to add fluoride to drinking water and Washington Water Service Company does not add any fluoride to any of its water systems.