We had a pond in our council house garden before we moved, the only thing our council stipulated was that the house and land was put back to how it was before we moved in.
Our neighbour isn't allowed to have a pond but she is child minder, this i can understand but the reason they have given you seems silly really, surely there is more bacteria and disease in your waste bin!
Maybe you could find a small, hidden patch in your garden, maybe near your ash trees 