Approved devices to protect against backflow or backsiphonage shall be installed at all fixtures and equipment where backflow and/or backsiphonage may occur and where there is a hazard to the potable water supply in that polluted water or other contaminating materials may enter into the public water supply. Any situation in which a heavy withdrawal of water, such as a sudden break in the main or water being used from a fire hydrant, may cause a negative pressure to develop that could lead to backsiphonage of polluted water into the system shall be improper and must be protected by approved backflow preventive valves and systems as determined by the Superintendent.