First, a labeled picture of the situation:


There are three ends, two in the ground and one in the house. How can I figure out which way the water is flowing?

There are four labeled valves (and one hose bib valve I left unlabeled). I'm guessing C and D are part of the pressure vacuum breaker, but I don't know what any of them are for. What is the purpose of each valve? Turning them all off does not seem to affect water in my house (I only ran water for about 15 seconds). Does that mean water is flowing out of my house at end 2 and into the ground at both ends 1 and 3?

Some additional context: this setup is on the back of my house. I have a pool and an in-ground irrigation system. There is a double check valve in front of my house that I would expect to control my irrigation system, but maybe it only controls the zones in front of my house (I'll be buying a valve handle soon to test it).

  • 1
    Is your water main even on this side of the house? i suspect its fed on the other side and the two pipes going to the ground (1&3) feed the irrigation(3) and the pool(1) from the one coming out of the house (2).When you turned all valves off and still had pressure in the house this was confirmed. C and D are the Irrigations pressure breaker. A is pool shut off. and B is shut off for irrigation... maybe...
    – mark f
    Oct 15, 2020 at 15:52
  • 1
    looks like the vacuum breaker is incorrectly installed ... valves B and C should not be there if they disable the vacuum breaker from operating for 1 and for the garden hose
    – jsotola
    Oct 15, 2020 at 16:00
  • The main is on the other side of the house, before the double check valve. I wouldn't be surprised if the PVB is incorrectly installed. If 1 is going to the pool, then the PVB was probably added after, when the irrigation system was installed, and they were too lazy or the owner didn't pay for them to reconfigure the existing pipe. Oct 15, 2020 at 16:16
  • B seems to be turned off, but my back sprinklers work. If I turn B on, water starts leaking out of the PVB. Does that mean the PVB is broken? Besides irrigation, where could that water be going? Oct 15, 2020 at 16:21
  • 1
    Nice job of labeling - it's made the discussion so much easier!
    – FreeMan
    Oct 15, 2020 at 17:44

1 Answer 1


In my area, it is common for PVB to break if incorrectly winterized, but local water code requires these to be installed and inspected annually, with an inspection report filed with the city water authority. I see duct tape on the PVB so this is likely cracked and causing the leak you mentioned in a comment.

I'd hazard a guess that water does come from the house at (2), flows toward (A), (B) and the hose bibb from there. You can verify this by closing (A) and (B) and running the hose bibb to ensure it still works. Run it long enough to be sure you have flowing water and not just clearing the pipe.

With (A) and (B) turned off, you can also test-run anything that you think is attached to them. Once the water in the pipes (1) and (3) is drained, they should no longer run (and if it's a pool and irrigation as suspected, you'd notice lack of pressure even before the lines are fully drained). You mentioned you may have a separate irrigation line so it's possible that one or both of these don't go where you expect. Specifically, if any of (B), (C), (D) are turned off and irrigation still runs, it's not fed from 3.

(B) (C) and (D) may seem redundant as they all feed or cut off the pipe (3). In my system, (B) is located inside the house to cut water off before it flows outside, so the system can be winterized. (C) and (D) are also for winterizing by pumping compressed air through each zone to clear out any water and prevent it from freezing. The shutoffs prevent air from escaping into the house as the lines are pressurized with air.

  • The duct tape is just to hold the insulation on. Based on the comment at 1:16 of this video, I'm concluding that the PVB broke during a freeze and that I need this kit to fix it (the leak is only out of the bonnet). I should have realized this earlier, but A and 1 go to my outdoor kitchen. All my sprinklers work with B closed, so 3 might go to my pool. I'll find out after I fix the PVB. Oct 16, 2020 at 19:11

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.