Can water siphon backwards through the house pressure regulator? My house is above the main water line in the street. If the main line pressure goes to zero, will the house water siphon backwards through the pressure regulator and down into the main line?

  • 1
    Do you know if you have a backflow preventer installed?
    – mikes
    Nov 8, 2013 at 22:29

2 Answers 2


If you have a backflow preventer, aka a check valve, installed in the system, then the water will not siphon back. This could be installed near the pressure regulator or main shutoff inside your home. It's also possible for the municipality to install one near the meter.

A standard pressure reducing valve closes when the water pressure inside reaches a threshold. Once the inside pressure drops slightly, the valve opens, at which point a backflow is possible.

prv diagram


Sure it will, though not as fast as it would going in the intended direction.

  • How does that work? If OP has a properly-installed check valve, you won't have any backflow, as it should have been designed. Without knowing OP's situation, this answer can't be considered complete.
    – alt
    Nov 11, 2013 at 15:54

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