Desmarais said while soluble sodium fluoride has traditionally proved easy to dissolve and add to the water supply, in recent years he is found that 40 percent of the product they have been buying will not dissolve, and he does not know why. Desmarais has sent the material out for testing on two separate occasions, but had no luck in determining what it contained. He has sent it back to the supplier and had a better quality product delivered following the complaint. But the next delivery presents with the same problem, he said. Never mind the fluoride toxicity issue. We all know about that. Show Less >>