Contaminants and Pollutants

How do the contaminants or pollutants get into the potable water supply?

During normal operations, pressure in the public water distribution system is adequate and providing a positive pressure to the customers. However, there are times when the pressure in the public water system distribution system change and in some cases drop to levels that could cause water to change the direction of flow. The water in the public water system could become sub atmospheric.

In this illustration, the storage tank is filled to a level by the incoming pressure in the public water distribution system. The water level in the tank will rise to a height relative to the incoming pressure.  This tank may be used for firefighting purposes and is classified as non-potable water.   If the pressure in the public water distribution system drops because of high water demands such as water being used to suppress a fire, the water level in the tank will drop because the pressure in the tank is greater than the pressure in the public water distribution system. The non-potable water in the tank in now being distributed throughout the pubic water distribution system and the consumers are drinking non-potable water. A backflow incident has occurred thus creating a cross-connection incident.