The water service line, the pipe running underground from the meter to your house, is the one part of your plumbing you never see. When it leaks, the water drains straight into the soil, and the symptoms show up indirectly: in your yard, your bill, and your water pressure. Because these leaks are invisible by nature, homeowners often chase the wrong cause for weeks. Here is how to read the signs correctly.
Last updated: October 13, 2026
How do I know if my underground water line is leaking?
Look for a cluster of these symptoms rather than any single one:
- Soggy or sunken spots in the yard, especially along the path from the meter to the house.
- One patch of grass growing faster and greener than the rest, even without extra watering.
- Low water pressure throughout the house, gradually getting worse.
- A water bill that keeps climbing with no change in usage.
- The sound of running water when everything is off, sometimes faintly audible near the meter or along the line's path.
- Cracks or settling in driveways, walkways, or patios above the line's route.
- Discolored water from taps, which can indicate a deteriorating line.
In Alhambra, many service lines are original to homes built decades ago, aging galvanized and copper lines are prime candidates for underground failure after years of soil movement and corrosion.
Rule out sprinklers first
This is the step most guides skip, and it prevents the most misdiagnosis. Irrigation systems leak too, stuck zone valves, cracked heads, and broken lateral lines create the exact same soggy spots and green patches as a service-line leak. Before suspecting the water line: run each irrigation zone and watch for geysers or pooling, then shut the irrigation off entirely at its own valve for a few days. If the wet spots dry up, the problem was irrigation. If they persist with the sprinklers off, the service line moves to the top of the suspect list.
Can a water meter detect an underground leak?
Yes, the meter test is the definitive do-it-yourself check. Turn off everything in the house and every irrigation zone, note the meter reading, wait one to two hours without using water, and read it again. Any movement means water is escaping on your side of the meter. To narrow it further, shut off the main house valve while leaving the meter-to-house line pressurized: if the meter still moves, the leak is in the underground service line between the meter and the house. That single test separates a service-line leak from every indoor suspect.
What does a leaking underground pipe sound like?
To the unaided ear, usually nothing, soil muffles the sound of escaping water, which is why these leaks stay hidden. But a ground microphone can pick up the hiss or whoosh of a pressurized leak through soil and pavement, and the loudest point sits roughly above the break. This is why acoustic listening is the primary professional tool for underground lines: it turns an invisible problem into a marked spot on the ground, so any digging is targeted instead of exploratory.
Will my yard always look wet if the water line leaks?
No, and this is why underground leaks go unnoticed for so long. A deep leak in sandy or well-draining soil may never surface; the water simply percolates downward, and the only symptoms are the bill and the pressure. Conversely, a shallow leak in dense clay soil shows up fast as a soggy patch. Do not wait for a swamp to appear before investigating, the meter test is far more reliable than your eyes.
What happens if an underground leak goes unfixed?
An underground leak does not fix itself, it gets worse. A small crack widens under constant pressure, the escaping water erodes soil around the pipe (which can cause settling under driveways and walkways), and the water bill keeps climbing every cycle. In the worst cases, prolonged saturation near the foundation can contribute to moisture problems inside the home. Because the leak is invisible, the damage compounds silently, which is why a positive meter test deserves prompt professional attention rather than a wait-and-see approach.
If the signs point to your service line, underground main line leak detection can pinpoint the break without tearing up the yard. Call +1 626-898-6221, Alhambra Leak Pros is open 24 hours.
Related service: Underground Main Line Leak Detection in Alhambra, CA
How pinpointing changes the job: 5 illustrative examples
The examples below are illustrative. They show how pinpointing typically changes a job. They are not reports of specific customer jobs, and they name no customer, address, date, or price.
1. A warm spot on the floor
Before: A homeowner notices one warm patch on the floor and a bill that keeps climbing, but no visible water. Without instruments, the only way to find the leak would be to open large areas of flooring and guess.
Method: The technician checks the meter, isolates the hot-water line, then combines thermal imaging with acoustic listening to follow the heat and sound to one point.
After: The leak is marked on the floor at one spot. Any repair opens that spot only, and the rest of the floor stays intact.
2. A stain on the ceiling
Before: A brown stain spreads across a ceiling, but the pipe above it may run several feet away. Opening the ceiling at the stain alone often misses the source and means opening more drywall later.
Method: The technician maps the damp area with thermal imaging and moisture readings, then checks pressure and nearby lines to trace the water back to its source.
After: The source line is identified and marked. Any opening is made where the leak actually is, not where the stain happens to show.
3. A meter that moves with everything off
Before: Every tap is off, yet the water meter still moves. That proves water is leaving the system somewhere, but it says nothing about where. Digging or opening walls at this point would be pure guesswork.
Method: The technician runs a timed meter test, then isolates lines one by one with pressure checks to narrow the loss to a single line.
After: The search area shrinks from the whole property to one line. Pinpointing then focuses on that line only, before anything is opened.
4. A pool that keeps losing water
Before: A pool loses water faster than normal, but some loss is normal evaporation. Draining the pool or digging up pipes without a test would waste water and money.
Method: The technician runs a bucket test to separate evaporation from a real leak, then pressure tests each line on its own to find which line loses pressure.
After: If the pool is only evaporating, no repair is needed. If one line fails, the search narrows to that line instead of the whole pool system.
5. Slow drains and a sewer odor
Before: Drains run slow and a sewer odor lingers, but the blockage or break could sit anywhere along the line. Digging to find it would disturb the yard and still might miss the defect.
Method: The technician sends a camera through an existing access point and watches the inside of the line on video, marking where roots, cracks, or offsets appear.
After: The defect is seen on video and its position is known. Any digging happens at that one place, after the cause is already clear.