Cross Connection Control Program Definitions

Cross Connections –any actual or potential connection between a potable water system and any source of pollution or contamination.


Backflow:  a flowing back or reversal of the normal direction of flow.

Backflow Explanation: It occurs when there is a difference in pressure (back pressure or back siphonage) in a continuous fluid system (i.e. your municipal water supply). Once backflow or back siphonage has ended, the flow of water in the distribution system will return to normal. Any backed water will now flow forward in the distribution system. Depending on how far back the contamination was pushed, it could be re-distributed to drinking water taps elsewhere on the property or to other properties in the neighborhood. When this water is re-distributed to drinking water taps, it may no longer meet the water quality standards that it did when it left the water treatment plant.


Back Pressure – pressure higher than the supply pressure.

Back Pressure Explanation: Pressure from a boiler or other pressurized system can overcome the pressure of the distribution system. Water from the boiler will be pushed back into the pipes of the distribution system, along with any chemical additives or bacteria that may have accumulated in the boiler.

Back Pressure Examples:

  • Boost pumps
  • Boilers with increased temperature
  • A private water supply system inter-connected with public water supply systems
  • Elevated tanks or other water pressure altering scenarios


Back Siphonage – backflow caused by pressure below atmospheric in the supply system.

Back Siphonage Explanation: Sometimes large water use in one part of the distribution system can result in less delivery pressure in another part of the distribution system. The delivery pressure drops so low that it is actually negative. Water is sucked back into the pipes of the distribution system along with any pollution or contaminants.

Back Siphonage Examples:

  • Breaks in a water main
  • Drainage of the water supply system for repairs
  • Shut-off of high-raised water supply
  • Nearby fire fighting



Please note: All definitions are as per the CSA Standard B64.10-11


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