9. McMurray, PA
Contaminants detected above health guidelines: 5
Pennsylvania American Water Pittsburgh serves around 507,675 consumers daily. Even though it has 5 contaminants that are above health guidelines, it is still one of the cities with the cleanest water in the US. Those contaminants are bromidichloromethane, chloroform, chromium, dibromochloromethane, and trihalomethanes.