From the link:
Fluoridation chemicals are unregulated, unpurified industrial-grade waste products from the phosphate fertilizer manufacturing industry, and the primary fluoridation chemical, hydrofluorosilicic acid (HFSA), is an EPA-rated Class One Hazardous Waste. These are not the same chemicals as the fluoride in toothpaste and other dental care products in the United States, which must be pharmaceutical grade and are subject to regulatory oversight.
The National Academy of Sciences and even fluoridation promoters acknowledge that HFSA is a hazardous waste byproduct from fertilizer manufacturing. HFSA is a highly acidic and corrosive liquid that is entirely different than the natural mineral calcium fluoride.
Note: hydrofluorosilicic acid is what is put into the Grand Rapids water supply.
To dispose of HFSA, the industrial manufacturer has to treat it as a hazardous waste, at significant cost. Because of its toxicity, it cannot be dumped into U.S. water systems, sewers, streams, rivers or the oceans. However, when a fertilizer manufacturer instead sells that same hazardous waste to public water agencies to add to our drinking tap water, it actually earns money. This creates a powerful incentive for industrial fertilizer manufacturers in the U.S. to maintain and fund efforts to promote water fluoridation.
More reasons below: