How Do You Find an Underground Sprinkler Leak?

Why the wet spot is not the leak

The instinct is to dig where the ground is soft. On a Piedmont clay lot that is frequently the wrong place, for two reasons.

First, clay does not let water percolate straight down. Water leaving a broken pipe follows the path of least resistance, which is usually along the pipe trench itself — the backfilled soil in that trench is looser than the undisturbed clay around it. Water can travel a long way down a trench line before it surfaces.

Second, slope. On a lot with any grade, water tracks downhill under the surface and emerges wherever the grade or a soil change forces it up. A leak at the top of a yard can surface at the bottom of it, twenty or thirty feet away and several feet lower.

So the wet area is evidence that a leak exists, and evidence of roughly which part of the property to investigate. It is not an X marking the spot, and treating it as one is how people end up with four holes and an unrepaired leak.

The diagnostic sequence

1. Confirm the loss at the meter. With every indoor fixture off and the controller not running, the meter should be completely still. If the low-flow indicator is turning, water is moving somewhere.
2. Isolate the irrigation system. Close the irrigation shutoff valve and read the meter again. If the movement stops, the leak is in the irrigation system. If it continues, the fault is on the house side and it is a plumbing call.
3. Test the mainline. With the shutoff open but the controller off, the mainline is pressurised and every zone valve is closed. Any flow in this state is a mainline leak or a valve that is not sealing — and those two are distinguished by whether water appears at a head.
4. Test each zone in turn. Run one zone at a time and watch both flow and pressure. A lateral break shows as unusually high flow with poor performance at the heads, and often as water surfacing while that zone alone is running.
5. Narrow the run. Within the suspect zone, the break is bracketed by watching where pressure and performance fall off along the line, and by following the pipe route from the valve outward.
6. Locate the pipe precisely. Valve and wire locating equipment finds the valve manifold and follows the field wire, which generally runs with the pipe. That converts a guessed route into a known one.
7. Excavate once. One targeted hole over the identified section, dug by hand around the pipe.

What the flow rate tells you

What homeowners can do before the appointment

• Run the meter test described above. Knowing whether the loss stops when irrigation is isolated is genuinely useful information and saves diagnostic time.
• Note which zone, if any, makes the wet area worse. Run each zone manually for a few minutes and watch.
• Photograph the wet area, ideally with something for scale, and mark it with a flag.
• Recall any recent digging — landscaping, fencing, a mailbox post, aeration, a utility trench. This is a common cause and it points the search immediately.
• Find the irrigation shutoff valve before you need it in a hurry.

Cost and access

Irrigation Medics bills $125 for the first hour on site and $80 per hour after, with parts separate and an estimate before digging. Leak repair covers the widest cost range of any irrigation repair because locating and access drive it far more than parts do. As a general North Georgia market figure, underground irrigation leak repairs commonly land between roughly $150 and $700 or more depending on depth, surface obstruction and how many breaks are found. Those are market estimates rather than quotes — see the cost guide.

The variable that moves the number most is what is above the pipe. Open sod is inexpensive to work in. A break under a driveway, a paver patio, a retaining wall footing or a mature root mass is a different job, and you will be told which one you have before work begins.

Terms used on this page

• Mainline. The pipe that carries pressurised water from the supply to the zone valves. It holds pressure all the time.
• Lateral line. The pipe from a zone valve out to the heads on that zone. It is only pressurised while that zone runs.
• Low-flow indicator. The small sweep dial or triangle on a water meter that turns on any flow, however small.

Related answers

• Why Is My Sprinkler System Leaking When It Is Turned Off?Water moving while the system is off means something on the pressurised side is failing, because the mainline holds pressure around the clock even…
• What Is the Difference Between a Mainline and a Lateral Line Leak?A mainline leak is on the pipe upstream of the zone valves, which is pressurised around the clock, so it wastes water continuously and is the more…
• Why Is There a Wet Spot in My Yard That Will Not Dry Out?A wet area that never dries is usually an irrigation leak, a valve seeping into a lateral, or water surfacing from a break further uphill. It can…
• Does Sprinkler Leak Repair Require Digging?Repairing a leak in a buried pipe does require reaching the pipe, so some excavation is unavoidable — but on a properly located leak that means one…
• Where Is My Irrigation Shutoff Valve?The irrigation shutoff valve isolates the sprinkler system from your water supply, and it is most often found near the water meter, at the backflow…

Services that fix this

Where we work

Irrigation Medics repairs irrigation systems across Hall County and the Lake Lanier communities, the Gwinnett corridor through Duluth, Suwanee and Buford, and North Fulton and Forsyth — Johns Creek, Alpharetta, Milton, Roswell and Cumming. Same rates throughout. See the service area.