Run each zone one at a time and look for soggy spots, bubbling soil, weak heads or water at the valve box. If the water meter moves while the sprinklers are off, the leak is in the always-pressurized mainline or a valve. If it only leaks while a zone runs, the break is in that zone's lateral line or a head.
A sprinkler leak can waste more water than every faucet in the house combined, and because the pipe is buried, it often goes unnoticed until the summer water bill arrives. Here’s how to track one down in your own yard, zone by zone.
Signs your irrigation system is leaking
- Soggy, spongy or sunken spots in the lawn, especially along a straight line
- Patches that stay greener than the rest of the yard
- Water bubbling or pooling near a sprinkler head or the valve box
- One zone with weak or uneven spray, or heads that don’t pop up fully
- The water meter moving while the sprinklers are off
- A jump in the water bill during watering season
Mainline or lateral line? The one test that matters
Before you dig, find out which part of the system is leaking. Most residential systems have two kinds of pipe:
| Pipe | Pressurized when? | What a leak looks like |
|---|---|---|
| Mainline (backflow preventer → zone valves) | All the time | Meter moves even with the sprinklers off; wet spot near the valve box or along the main run |
| Lateral lines (valve → heads) | Only while that zone runs | Soggy spot or weak pressure in one zone, only during or after watering |
The test:
- Make sure the sprinklers and all indoor water are off.
- Check the water meter for 15–30 minutes.
- Close the irrigation isolation valve, usually near the backflow preventer or where the irrigation tees off the main water line.
- If the meter stops, the leak is in the irrigation mainline or a valve. If it keeps moving, the leak is in the house or the main service line. See how to find an underground water leak.
How to find the leak zone by zone
- Turn on one zone manually from the controller.
- Walk the zone and watch each head. Look for geysers, heads that barely rise, water seeping around a head’s base, and wet soil between heads.
- Listen near the valve box. A hissing valve that doesn’t fully close points to a worn diaphragm or debris in the valve.
- Let it run for 10–15 minutes, then walk it again. Slow leaks often show up as a spreading wet patch after a few minutes.
- Repeat for every zone and note which one has the problem.
Tip: Mark suspicious spots with a flag or a screwdriver as you go. After all the zones have run, the pattern usually points to one pipe run.
Check the valve box and backflow preventer
Many irrigation leaks aren’t in the pipe at all:
- Valve box full of water: a leaking valve body, a loose fitting, or a cracked solenoid seal.
- Weeping valve: a zone that keeps dribbling after it shuts off usually has a worn diaphragm.
- Backflow preventer dripping or split: common after a freeze if the system wasn’t drained completely.
Why spring start-up is when most leaks show up
In central Indiana, sprinkler systems are usually winterized each fall by blowing the lines out with compressed air. Any water left in a low spot, fitting or backflow preventer can freeze, expand and crack the part. Those cracks stay hidden until the system is pressurized again in spring. That’s why the first run of the season is the best time to walk every zone.
When a sprinkler leak needs professional detection
DIY checks find most broken heads and obvious wet spots. Call a professional when:
- the meter shows a mainline leak but there’s no wet spot,
- the leak is under a driveway, patio or landscaping you don’t want to dig up,
- the soil drains so well that water never surfaces, or
- you can’t tell whether it’s the sprinkler line or the main water line to the house.
Our irrigation leak detection service tests each zone, checks the valves and traces the buried line with acoustic equipment, then marks the break so only a small hole is dug. We cover Bargersville and the rest of Johnson County.
Sprinkler leak checklist
- Meter test with sprinklers off (mainline check)
- Close the irrigation isolation valve and retest
- Run each zone and walk it twice
- Inspect the valve box, valves and backflow preventer
- Flag every wet or weak spot
Still can’t find it?
Our irrigation leak detection pinpoints the leak without tearing things up, so the repair starts in the right spot.
Frequently asked questions
How do I know if my sprinkler system has a leak?
Common signs are soggy or unusually green patches, water bubbling from the soil, one zone with weak spray, water in the valve box, and a water meter that moves while the system is off.
What's the difference between a mainline and a lateral line leak?
The mainline runs from the backflow preventer to the zone valves and stays pressurized all the time, so a mainline leak wastes water even when the sprinklers are off. Lateral lines run from each valve to the heads and only carry water while that zone runs.
When should I check my sprinkler system for leaks in Indiana?
At spring start-up, after the system has been winterized, and any time your summer water bill jumps. Freeze damage over the winter is one of the most common causes of irrigation leaks in central Indiana.
Can a sprinkler leak be underground with no wet spot?
Yes. In sandy or well-drained soil, water can drain away without pooling. Watch for a zone that loses pressure, a patch that stays greener than the rest, or a meter that moves with the system off.