You've hit the nail on the head with regard to the problem utilities face. I mentioned Regina, and they are very reluctant to add phosphate for this very reason. They discharge their waste water into a river system. Blue-green algae would be a top priority for them.
Other chemicals could be carbonates or silicates, or there could be pH adjustment, which Ottawa does. They adjust their pH to a much higher level. Each utility would have almost a unique, tailored program. The phosphate issue is an important one for many utilities in Ontario and certainly in western Canada.