Signs of a Leak in an Irrigation System

What are the most common signs of an irrigation leak?

Soggy ground or standing water that never dries, a patch of lawn that is greener and faster-growing than the rest, heads that are weak or will not pop up on one zone, water bubbling up around a head or valve box, sunken soil along a pipe route, and a water bill or meter reading that climbs without a schedule change. Our sprinkler repair page puts the bill clue simply: a high bill while the lawn still looks dry usually points to a leak on the pressurized side, where water escapes underground instead of reaching the heads.

EPA WaterSense's Sprinkler Spruce-Up adds two that people miss: water pooling on the surface between watering cycles, which can indicate an underground leak, and valves that do not close fully and seep water even when the system is off.

Why are irrigation leaks so hard to spot?

Timing and location. EPA notes that broken heads are hard to spot because systems often run overnight or early morning, when nobody is watching. Pipes are buried, and in gravelly western Montana soils, water from a cracked lateral can drain away downward without ever surfacing. Colorado State University Extension's drip guide adds that leaks at ground level on drip systems are hard to see, and suggests flow indicator devices to help. The fix is to watch the system run deliberately, a zone at a time, a few times each season.

What does a soggy spot that never dries mean?

Usually a leak downstream of a valve: a cracked lateral pipe, a broken fitting, or a riser snapped below a head. Our sprinkler repair page notes that a permanently soggy patch generally means exactly that. If the soggy area is right around a valve box, the valve itself or its fittings are the suspect. If it sits along a straight line across the lawn, it is likely the pipe. If it is around a single head, look at the head, its riser and the swing joint underneath.

What if one area is wet even when the system is off?

Then water is getting past a valve that should be closed, or there is a leak on the mainline, which stays pressurized all season. EPA's spruce-up advises checking valve box connections and notes that valves that do not close fully can seep even when the system is off; the lowest heads on that zone will usually weep after every cycle. Rain Bird's troubleshooting guide lists debris caught in the diaphragm, a worn or damaged diaphragm and solenoid failure as the causes of zones that keep running, and says such zones waste significant water.

A mainline leak is the more serious version, because the mainline is under pressure whenever the system is on for the season, not just when a zone runs. That is the leak that shows up as a steady climb on the meter.

How do you use the water meter to check for a leak?

Turn off every indoor and outdoor use, leave the irrigation system on for the season but with no zone running, and watch the meter. If it moves, water is going somewhere. Then close the irrigation shutoff and watch again: if the movement stops, the leak is in the irrigation system rather than the house. If you are on Missoula Water, the newer meters make this easier. The city says its AMI meters transmit readings every 15 minutes, and that once the customer portal is available, customers can see daily and hourly use and set alerts for continuous flow, which often indicates a leak.

On a well, the pump is the meter. A pump that kicks on when nothing in the house or yard is running is telling you the same thing.

Where do leaks usually happen on Montana systems?

At the places that take abuse. Rain Bird lists damage from mowers and vehicles, cracked housings, broken risers and poor thread sealing as the usual causes of leaks at heads. On Montana properties, add snowplows and snow piles along driveway edges, frost heave that lifts and tilts heads, and the freeze damage that happens when a system is not winterized. CSU explains that water expands by about one-eleventh of its volume as it freezes, which is what splits fittings, valve bodies and backflow assemblies left with water in them.

Freeze damage often hides until spring. Our sprinkler blowout and winterization page notes that it shows up when the system is turned on in April, and the spring startup guide explains how to find it before it wastes a summer's water.

Can leaks cause low pressure?

Yes. Water escaping from a break reaches the ground instead of the heads, so heads beyond the leak run weak or fail to pop up. Rain Bird lists leaking pipes or fittings among the causes of low pressure. If one zone is suddenly weak and part of it is soggy, a leak is the first suspect. Our low water pressure guide covers the other causes.

What about leaks at the backflow preventer?

Water dripping or spraying from the backflow assembly needs attention quickly, partly because it is your protection against contamination and partly because, in Missoula, a repaired assembly has to be retested. Missoula Water's program requires a test by a certified tester immediately after any repair, and says unserviceable assemblies must be repaired or replaced. An RP assembly that discharges from its relief valve is telling you something is wrong with its checks. Our backflow testing guide explains the rules.

Do hoses and faucets count?

They do. The City of Missoula's conservation page advises checking hoses, pipes, faucets and connections for leaks, and notes that a faucet dripping a single drop per second can waste about 2,400 gallons a year. A hose bib that drips all summer behind a shrub adds up the same way, and a frost-damaged one can leak inside the wall.

How often should you check for leaks?

EPA WaterSense's watering tips recommend inspecting the irrigation system monthly for leaks and broken or clogged heads. A practical routine is a full walk at spring startup, a quick run of each zone once a month through the season, and a look at the meter whenever the bill jumps. Write down what you find so you can tell whether a wet spot is new.

Can you narrow down a leak yourself?

Often you can get most of the way. Run one zone at a time in manual mode and watch it for a full cycle, then walk it again 30 minutes after it shuts off. Note any head that runs weak, any spot where water bubbles up, and any area that stays wet while the rest of the zone dries. Open the valve boxes and look for water standing in them or seeping around the valve body. Press on the turf along the pipe route; soft, spongy ground over a line is a strong hint.

If one zone weeps after it shuts off, the leak is probably at or after that zone's valve, or the valve is not closing. If the ground is wet with no zone running at all, suspect the mainline or the backflow assembly. If the meter moves with everything off and the irrigation shutoff closed, the leak is in the house plumbing rather than the sprinklers. Any of those notes will make a repair visit faster and less invasive, because we can dig in one place instead of several.

When should you call for repair?

As soon as you see a sign you cannot explain, because a leak never gets cheaper. We locate leaks before we dig, repair laterals, mainlines, valves and heads, and tell you what can wait. This guide is part of our Montana Landscaping, Lawn & Irrigation Guide, and our irrigation systems page explains how we maintain systems through the season. Call HJ Property Care & Tree Service at (406) 215-7319 or request a free estimate. We work across Missoula and Ravalli counties, from Missoula and Lolo to Florence, Stevensville, Corvallis, Victor, Hamilton and Darby.

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