How do I find a leak when I cannot see it above ground?

I moved into a home two years ago with a fully installed and operating irrigation system. From the start, I noticed that on a regular basis, small 4-8" sections of my lawn would collapse 6-10". Maybe a couple dozen of them. I’d fill the depressions with rocks, dirt, sand, and it would recur.

#1 At first I thought it was critters. Nope. #2, There is a septic leaching field under some of the area of concern. Had a septic guy out and verified my leaching field is working properly. #3 I have an irrigation zone which runs over the top of it, for about 100 feet in length. The sprayer heads all operate and no visible leaks. I slapped a pressure gauge on the faucet adjacent to the irrigation feed (I realize this is system pressure, but there will still be change), and compared it to what the pressure is when a different zone is operating. The system PSI is down to less than 5 when the suspect zone is operating. The other zones only bring the psi down to about 40, and the non running psi is nearly 100.

We have not been using the system this year due to a construction project. No new holes.

My hypothesis is that the zone pipe is leaking somewhere, but the water is being absorbed by the septic leaching field.

** The holes are NOT coincident with the sprinkler heads or the presumed pipe location. **

How do I find a leak when I cannot see it above ground? It’s a high-end lawn, and the engineer in me says “try to narrow it down further without digging”. Is this possible?

I’m thinking about making small holes near each spray head and seeing if the pipe or soil is wet. I’d rather not start ripping it up until I find it.

  • or -
    What about removing all the heads and replacing them with a home-brew standpipe, which effectively shuts off the head? The hope would be the increased pressure would force more water out of the leak itself and make it visible.
    Am I dreaming?


Finding leaks is a pain. Are you sure it’s not critters? I was troubleshooting a zone that had no water pressure and was digging holes to find it because there was no excess water appearing anywhere. I eventually found a riser that had a larger bite taken out of it about half an inch wide. There was a cave dug out under ground leading right up to that sprinkler that must have gone very far because the water just drained into it and disappeared.

I like your idea of capping all the sprinklers to check for leaks, that might help unless you have an under ground cavern like I did. If theres a better way without digging I haven’t figured it out. Typically sprinklers are going to break in 2 places, the riser, or the pipe joints. Good luck!

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I like your story! I’ll bet you have groundhogs. Only burrowing animal I know that’s strong enough. I have moles and chipmunks only.

Based on your suggestion, im gonna dig out around the risers. If it’s leaking there it must be undermined. I hope!
Thanks! :slight_smile:

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