Underground leak vs irrigation leak
A wet spot in the yard usually comes from one of three things: the buried water service line, the irrigation network, or rain and drainage with no pipe behind it. Timing and meter observations help separate the possibilities.
Brisbane Leakmark guides
Why is it hard to tell them apart?
Outdoors, water rarely surfaces right above its source. It follows trench backfill and the slope of the lot, then appears at a low point. Two pressurized systems often share the same ground, and storms add water with no pipe behind it. A single wet patch is a starting point. What you need is a pattern: when it’s wet, and what the meter is doing at the time.
Service line or sprinkler?
In many residential systems, household supply and irrigation share a potable-water meter. Other properties may have a separate irrigation meter or non-potable supply. Confirm your setup before interpreting meter readings.
| Private water service line | Irrigation network | |
|---|---|---|
| Purpose | Feeds the building’s taps and fixtures | Feeds sprinklers, drip lines or bubblers; may have a separate meter or water source |
| When it’s pressurized | All the time | Pressurized up to the valves all the time; zone pipes only while a zone runs |
| Typical route | Meter to the building’s entry point, often in one run | Branches off toward planters, lawns and beds |
| Control | Building main shutoff | Controller (timer), backflow device and zone valves |
| How a leak behaves | Steady, around the clock | Often worst during or just after a watering cycle |
That last row is the most useful one. One caution: the irrigation pipe between the house supply and the zone valves stays pressurized all day. A leak there behaves like a service-line leak, even though it belongs to the irrigation system.
Does the wet ground match the sprinkler schedule?
Suspect irrigation first when:
- The spot is wet in the morning after an early cycle and drier by evening
- Water bubbles or pools near a sprinkler head, drip emitter or valve box while a zone runs
- One zone shows weak spray or misting heads while others look normal
- The wet area sits inside a planting bed or lawn the system waters
Write down which zone was running and when. That detail saves time later.
What if the yard stays wet when sprinklers are off?
Suspect the service line, a buried branch or the pressurized part of the irrigation supply when:
- The ground stays wet after the controller has been off for two or more dry days
- The wet strip lines up with the path from the meter toward the building
- Water appears at a driveway crack, path edge or retaining wall far from any sprinkler
- The area never fully dries, even in warm weather
Meter observations that may help
The meter can’t name the system that’s leaking, but it can narrow the field.
- Meter moving with every fixture off and the controller off? Water is leaving somewhere downstream of the meter.
- Movement appears only while a zone runs, beyond normal flow? That’s hard to judge by eye. Note it and let a professional interpret it.
- Meter still with everything off? A constant supply leak is less likely. Look harder at drainage, rain or a zone-only irrigation leak.
Only read the meter if its box opens easily and safely, and never operate the utility’s valve. Our water meter guide covers reading the dial step by step.
Pressure and sprinkler-zone changes
Weak pressure indoors as well as outside can come from a large leak on the shared supply, but also from a partly closed valve or a pressure regulator problem. Weak spray in one zone only points to that zone: a cracked lateral, broken head or valve fault. A zone that won’t shut off fully, or keeps weeping after its cycle ends, often means a valve isn’t sealing.
Weather runoff and drainage alternatives
| Clue | Buried service line | Irrigation system | Rain, runoff or drainage |
|---|---|---|---|
| Timing | Wet regardless of schedule or weather | Linked to watering cycles | Appears during or after storms |
| Location | Along the meter-to-building route | In or near watered areas | Low points, slope bases, downspout outlets |
| Meter with all use off | Usually moving | Still, unless the pressurized supply leaks | Still |
| Dries out when | Often remains wet while loss continues | Can improve when a leaking zone or supply is isolated | May fade with drier weather |
Rain can blur the picture. Compare with earlier dry-weather observations if available, but do not wait through continued water loss or growing property damage. Water color alone cannot distinguish the source.
What pipes may be buried beneath the yard
- Water service line: meter to the building
- Branch lines: to hose bibs, garages, outbuildings or a second unit
- Irrigation supply: from the house supply to the backflow device and valve manifold
- Zone laterals: from each valve out to heads or drip tubing
- Drain and sewer laterals: wastewater lines, not pressurized
- Downspout and yard drains: storm water only
Those utilities, plus gas, electric and communications lines, are the main reason never to dig for a leak yourself. California AB 1572 phases in restrictions on potable-water irrigation of nonfunctional turf for public, commercial/industrial/institutional, and HOA common-area properties — it does not establish that your wet area is caused by irrigation.
What to note before shutting anything off
- Photos of the wet area and its edges, with the date and time
- The controller’s current schedule (zones, start times, run times)
- The meter reading and leak indicator, if you can view them safely
- Where the backflow device and valve boxes are
- Recent landscaping, planting or hardscape work
Why controllers complicate testing
Controllers aren’t always as “off” as they look. Rain delays expire, seasonal adjustments shift start times, and some models run a second program. A valve can also weep with the controller fully off. So “the timer is off” only removes scheduled watering — it doesn’t rule irrigation out. The City of Brisbane’s water conservation page links to a Water Calculator with guidance on setting irrigation controllers.
When municipal main trouble is possible
Treat it as a possible public-system problem if:
- Water is rising through the roadway, curb line or a public walkway
- The meter box is flooded or the meter is visibly leaking
- Several neighboring properties report wet ground or pressure loss at once
In those cases, contact City of Brisbane Public Works at 415-508-2130 rather than a private provider. See city water main vs private property leak.
Safe observations without digging
- Record how the spot changes, using observations already available. If water is pooling or damage is spreading, pause the suspected irrigation zone rather than continuing to water just for a test.
- Run one zone at a time from the controller, if it allows manual runs, and watch the suspect area.
- Look for surface signs along the likely service-line route: soft ground, sunken spots, greener strips.
- Check valve boxes visually for standing water, if the lids lift without force.
- Record what you see in photos at the same time each day.
Avoid probing with metal rods, trenching or lifting pavers. Buried utilities, pipe damage and permits are all real risks.
When to request specialized outdoor detection
| Your observations | Suggested next step |
|---|---|
| Wet only after watering, single zone | Irrigation leak detection |
| Wet with irrigation off for days, meter moving | Underground water line leak detection |
| Wet with irrigation off, meter still | Consider drainage, runoff, sewer, and intermittent or separately metered irrigation leaks |
| Water in the street or at the meter box | City of Brisbane Public Works |
| Mixed or unclear pattern | A professional investigation that tests both systems |
How subsequent repairs differ
Irrigation repairs usually involve heads, laterals, valves or the backflow device, and may need a landscape or irrigation specialist. Service-line repairs involve the potable supply to the building and can mean excavation, permits near the street and utility marking. See underground water line repair and irrigation leak repair.
Outdoor water-loss FAQs
Can a sprinkler leak continue when sprinklers are off?
Yes. The pipe between the house supply and the zone valves stays pressurized, and a valve can weep even when no zone is scheduled. Either can keep soil wet with the controller off. A leak downstream of a valve usually shows up only while that zone runs.
Will a broken service line cause low pressure?
A large break can, especially at fixtures far from the meter. Small leaks often cause no noticeable pressure change. Low pressure also has other causes, such as a pressure regulator problem or a partly closed valve.
Can the water meter help separate systems?
Partly. Meter movement in a genuine no-use period indicates flow through that meter, but it cannot identify which buried pipe or tell you about a separately metered irrigation system. Interpreting small changes reliably usually takes a professional.
Is wet soil always due to a pipe failure?
No. Rain, slope runoff, downspouts and poor drainage often wet soil with no leak involved. Clear water, wetness during dry spells and a moving meter make a pipe more likely. Muddy water that appears after storms and fades in dry weather usually isn’t a leak.
Should I excavate the wet spot myself?
No. Gas, electric and communication lines may be buried nearby, and digging in California requires 811 utility marking first. The wet spot is often not above the leak anyway. Leave excavation to a qualified contractor.
Who handles suspected leaks in the public street?
Water rising through the roadway or a public walkway goes to City of Brisbane Public Works first. If the City traces the source to your property, a private investigation picks up from there.
Get help identifying the right system
If your notes still point both ways, or the meter keeps moving and you can’t tell why, a professional investigation can test the buried supply and pin down what you’re dealing with. Irrigation work is handled only where the appropriate service is available.
Call (415) 532-1415Still not sure which system it is?
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