I would be concerned about chlorine as well, i've heard that some water districts also add fluorine which is even worse for little fishys.
i might experiment with a bucket and a fish to see at what volume added the fish croaks.....you might be able to add some (city water) if you let it run overland a ways to degas the chlorine, oxygenate, and come up in temp. some before mixing w/ pond water.
