According to the Manchester Water Works Water Supply Manager David Paris, Manchester does add hydrofluorisilicic (HFS) acid and not pure fluoride to its water supply. Paris
is not sure, but it is very likely the compound is a by-product of the fertilizer industry. Paris
also confirmed the presence of arsenic and lead in the HFS acid, but he
said the compound is highly processed and purified, making it safe for human consumption. He
also said Manchester
actually made its standards for levels of arsenic and lead more stringent when they began the fluoridation in Manchester
said fluoride is too unstable as a pure compound and HFS is actually the least dangerous way to add it to drinking water, as well as being the most cost effective.