Fluoridation During Municipal Water Treatment
Municipal water treatment is very similar to a manufacturing process where the composition of the final product must meet certain specifications, many of these prescribed by regulation. There are several steps in the DMWW process: coagulation and sedimentation to remove dirt in the river water, hardness reduction, filtration, nitrate removal, disinfection, and fluoridation.
DMWW source water (Raccoon and Des Moines Rivers, and shallow groundwater under river influence) contains some fluoride, usually between 0.1 and 0.5 part per million (ppm). This is increased to about 1 ppm by addition of fluorosilicic acid. There are other ways to add fluoride, most notably with sodium fluoride. Fluorosilicic acid can be added in the liquid form, which is mechanically simpler than adding solid sodium fluoride. Fluorosilicic acid is the most economical vehicle for fluoride addition.
Fluorosilicic acid is a co-product formed during the production of fertilizer. Phosphate rock used to produce fertilizer contains significant amounts of fluoride. This is recovered as fluorosilicic acid and used in water treatment, brewing, and other applications. Like all chemicals used for municipal water treatment, fluorosilicic acid must meet stringent requirements for composition and impurities.
The addition of fluorosilicic acid to the water is monitored every minute of every day by DMWW staff, so that the proper amount of fluoride is always maintained in the drinking water delivered to your home.