What is a cross connection?
A cross connection is a point in a plumbing system where the potable water supply is connected directly or can be connected directly to a non-potable, potentially lethal source. Wherever an unprotected cross connection exists, backflow may occur due to either back siphonage or back pressure, causing pathogenic microorganisms to be carried into the potable water supply. Back siphonage is caused by a negative or reduced pressure in the supply line to a facility or plumbing fixture. The principle causes of back siphonage are:
  • High velocities in pipe lines that create a venturi effect
  • Water main line repair or break which is lower than a service point
  • Lowered water main pressure due to high water withdrawal rates such as fire fighting or water main flushing
  • Reduced water main supply pressure on suction side of a booster pump

Back pressure may cause backflow to occur whenever a potable water system is connected to another system operating at a higher pressure. The principal causes of back pressure are:

  • Booster pumps in the private plumbing system designed without backflow prevention assemblies
  • Potable water connections to boilers and other non-potable pressure systems
  • Interconnection with another plumbing system operated at a higher pressure
  • Water piping extending 30 feet above finished grade

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1. Why should I be concerned about cross connection?
2. What is a cross connection?
3. Where are cross connections found?