Key takeaways
- The mainline is under constant pressure and leaks continuously; laterals only leak when their zone runs.
- Isolate the irrigation at its own shutoff and re-test the meter to confirm the loss is on the irrigation side.
- A pressurized mainline can be located acoustically with a correlator just like a service line.
- A valve box full of water with the system off is a classic mainline or valve leak sign.
Mainline or lateral?
An irrigation system has two kinds of pipe. The mainline runs from the backflow assembly to the valve boxes and is under pressure all the time. The laterals run from each valve to the heads and are only pressurized when that zone is running. A leak on the mainline runs constantly and shows up on the meter around the clock. A leak on a lateral only runs during its zone's cycle, which makes it harder to catch on the meter but easier to see: a weak zone, a head that won't pop, or a wet spot that appears on watering days.
Confirm it's irrigation
Close the irrigation's own shutoff, usually at the backflow assembly, and do the meter test. If a continuous low-flow reading stops when the irrigation is isolated, the leak is on the irrigation side. If it continues, it's the house service line or the house, and the irrigation is innocent.
Finding a mainline leak
A pressurized mainline is located acoustically. The route is traced, a correlator is placed across the run where there are access points, and the ground microphone pinpoints the break. Valve boxes are checked along the way, because a valve that's weeping from its bonnet or diaphragm will fill the box with water and is the leak more often than people expect.
Finding a lateral leak
Run the suspect zone and walk it. Look for a head that doesn't rise, a head that gushes instead of sprays, a soft spot, or water pooling at a low point. Lateral breaks are usually at fittings, at heads that have been hit by a mower, or where a line passes under a driveway. With the zone running, the ground microphone finds them too.
Repair
Most irrigation repairs are a cut-and-couple on poly or PVC, a replaced fitting, or a rebuilt valve, and the turf goes back the same day. An older mainline that is failing in several places is better replaced than patched repeatedly.
Written by the crew at 360 Leak Finders
We locate, excavate and repair buried water lines and exterior drains across Kitsap County, 24 hours a day. If this guide raised a question about your property, call (206) 354-9906.