Approved devices to protect against backflow or back siphonage shall be installed at all fixtures and equipment where backflow and/or back siphonage may occur and where there is a hazard to the potable water supply, in that polluted water or other contaminated 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 which could lead to back siphonage 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 of Public Works. (Ord. 936, 1-7-1991; amd. 1998 Code)