Locating method
Leak Detection
Pinpoint the leak, dig one hole instead of the run.
Acoustic correlation, ground microphones, tracer gas, and pressure testing used to pinpoint where a pressurized water or gas line is losing product. The output is a marked point small enough to excavate, not a trench down the length of the line.
What Leak Detection is
Leak detection is the work of finding exactly where a pressurized line is losing water or gas, so the repair becomes one small excavation instead of a trench along the whole run. It is a separate discipline from locating: locating answers where the pipe is, leak detection answers where the pipe has failed, and most jobs need both, in that order. The same toolkit serves two very different customers, municipal water systems chasing non-revenue water across miles of distribution main, and property owners with a service line, slab, irrigation zone, or yard gas line losing product on their side of the meter. Because escaping water travels along the pipe bedding and often surfaces far from the failure, or drains away into a storm line without ever showing at grade, the visible wet spot is an unreliable guide and instrumentation is what actually narrows the search.
How it works
A leak in a pressurized line makes noise as fluid is forced through a small opening, and that vibration travels along the pipe wall and out through the surrounding soil. A ground microphone or geophone reads that vibration from the surface while the locator walks the line, listening for the point of peak amplitude. Leak noise correlation places a sensor at two contact points on either side of the suspected leak, usually valves, hydrants, or meters, and cross-correlates the two recordings; the time offset between them, combined with the distance between sensors and the sound velocity for that pipe material and diameter, puts the leak at a calculated position between them. Tracer gas takes a completely different route: the line is isolated, drained, and charged with a nitrogen and hydrogen blend, conventionally 95/5, which carries no oxygen of its own and dilutes with air to below hydrogen's lower flammability limit before enough oxygen is present to support combustion, which is why the blend is classed non-flammable, and because hydrogen is the smallest molecule it escapes at the failure and diffuses up through soil and pavement joints where a surface probe picks it up. Thermal imaging reads the surface temperature contrast created by escaping water and is strongest on hot water lines under slabs. Pressure decay and step testing sit ahead of all of it, confirming that a section leaks and roughly how badly before anyone spends time pinpointing; on distribution systems that usually means valve-by-valve step testing or minimum night flow monitoring in a district metered area to narrow the loss to a block.
When to choose Leak Detection
Choose leak detection when you already know roughly where the line runs and need to know where it failed: an unexplained jump in consumption, a meter that keeps turning with every fixture shut off, a soft or sinking spot in a lawn or parking lot, warm flooring over a slab, or an irrigation zone that will not hold pressure. It is also the standard approach for municipal water-loss programs, where surveying mains and services is far cheaper than replacing them on suspicion. On plastic and low-pressure lines, where the acoustic signal is weak or absent, tracer gas is usually the method that succeeds. If the line itself is unmapped, have it located and marked first, because both the correlator and the ground microphone depend on knowing where to place sensors and where to walk.
What Leak Detection is used for
- Municipal water main and distribution leak surveys
- Non-revenue water and minimum night flow investigations
- Private service line leaks between the meter and the building
- Slab leak pinpointing under residential and commercial floors
- Irrigation mainline and zone leaks on farms, parks, and courses
- Yard and building gas line leak checks past the meter
- Post-repair verification and pressure testing of isolated sections
What Leak Detection cannot do
Every technique here has conditions that defeat it. Acoustic work depends on the pipe carrying sound: cast iron, ductile iron, steel, and copper transmit a leak signal well, while PVC and HDPE damp the higher frequencies that carry it and large-diameter mains attenuate it quickly, so usable correlation distances shrink and false peaks become common. Correlation is also only as good as its inputs; a wrong pipe material, a wrong diameter, or an unrecorded length or bend between sensors shifts the calculated position, sometimes by many feet. Ground microphones are degraded by traffic, wind, pumps, HVAC equipment, and footsteps, and they read far better through pavement than through loose soil, gravel, or landscaped ground, which is why municipal survey work is often done at night. Tracer gas requires the line to be isolated, drained, and accessible for charging, and the gas can migrate along trench bedding or under pavement and surface some distance from the actual failure. Thermal imaging reads surface temperature only, so it is much weaker on cold water lines than on hot, and it is easily confounded by solar loading, reflective finishes, floor coverings, and radiant heating. Pressure and step testing prove a leak exists and how large it is but do not pinpoint it on their own, several simultaneous leaks confuse every acoustic method, and none of these techniques apply to gravity sewers, which are investigated with camera, smoke, or dye testing instead. Finally, a pinpoint is a place to start digging, not a guarantee of what is in the hole, so the excavation still has to be opened carefully and with current utility marks in place.
What Leak Detection finds
Looking for one specific line rather than a technique? Each of these covers what the utility is, why it is hard to find, and what one-call does and does not mark.
Questions
Leak Detection FAQ
Does leak detection replace calling 811 before I dig?
No, and the two do different jobs. Call 811, or your provincial one-call center in Canada, before any excavation; it is free, it is required by law in most jurisdictions, and it gets the public utilities marked up to your meter. One-call does not find leaks and does not mark anything on the private side of the meter, which is where most service line, irrigation, and yard gas leaks are. Use both: one-call for the public lines, and a private locating and leak detection company for your own lines and for the pinpoint. If you smell gas at any point, leave the area first and call your gas utility’s emergency number or 911.
My water bill jumped but nothing is wet. Can a leak still be found?
Usually yes. Shut off every fixture and watch the meter; movement with nothing running is strong evidence of a leak on your side of it. Escaping water often runs along the pipe bedding and surfaces well away from the break, or drains into a storm line, sewer, or porous fill and never shows at grade at all, so the absence of a wet spot tells you very little. A locating and leak detection company traces the line first, then uses a correlator, ground microphone, or tracer gas to narrow the loss to a point you can dig.
Does leak detection work on plastic water lines?
It works, but not as easily. PVC and HDPE absorb the higher-frequency sound that carries a leak signal along metal pipe, so acoustic range is much shorter and small leaks can go unheard, especially on large-diameter or deeply buried line. Hydrophones that couple into the water column at hydrants and valves recover part of that signal, and tracer gas is the usual fallback because it does not depend on pipe material at all. Say what the pipe is made of when you request a quote, because it changes the equipment the service provider brings.
What does a leak detection job cost?
It is quoted per job rather than off a rate card, because the work scales with how much line has to be surveyed, what surface it runs under, how accessible the valves and meters are, and whether isolation, tracer gas, or night work is needed. Submit the job once through Utility Hotline and local service providers send you their own quotes so you can compare. Including the pipe material, the approximate length of the run, and what you have already seen at the meter gets you more accurate numbers.
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