Although I've not seen the pool officials admit that they are using copper sulfate in their pool water, other clues make it appear obvious that they are. For example, aqueous copper stains pale ...

eg electrolysis of aqueous sodium chloride or aqueous copper sulfate solution Production of salts, eg production of pure dry sample of a salt Use a balance to measure the mass of the copper ...

Zinc sulfide is made into an aqueous solution, before a highly diluted copper sulfate solution is added, along with ammonium chloride to act as a flux. The mixture is stirred, before being heated ...