Why Backflow Occurs 7

Knowing the location of low pressure in the public water distribution system is critical to part of the cross-connection control program. Those service connections that are located within the danger zone are the service connection that would most likely be impacted by low pressure during peak demands. Backflow is most likely to occur in the danger zone when the pressure decrease because of high water demands during peak water use days. .  The public water system should be aware of the peak demands during the day and months. If the demands do not exceed the peak demands and fire flows can be met, the likelihood of a cross-connection incident occurring from unprotected cross-connection is low. However, if the demands exceed the peak demands and fire flows are an issue, the probability of a cross-connection incident occurring from an unprotected cross-connection is likely.  All cross-connections shall be controlled not matter what the pressure issues are within the distribution system. However, those public water systems that have pressure concerns in the distribution system are more vulnerable to having a public health issue due to backflow of non-potable water into the potable water system from unprotected cross-connections. As show in this illustration, those building that are located within the danger zone will be without water if the water pressure drops below normal. A public health threat will be created within the domestic water system of the building located within the danger zone.  Every public water system should know and map out the pressure danger zone.