Updated On 05/06/2026
A leaking sewer line is one of the harder home problems to catch early. The pipe is buried, the leak is usually slow, and the symptoms it produces at the surface — a soft patch in the lawn, a faint smell in the basement, a water bill that creeps up — are easy to attribute to something else. By the time most homeowners are confident they have a leak, the line has been leaking for months.
This guide covers two things. First, the signs that point to a sewer leak and what each one is telling you. Second, how leak detection works once you’ve called a professional — the methods, the equipment, and what a competent inspection should produce. If you are already past the “is something wrong” stage and trying to figure out what to do about it, the second half of the post is where to start.
Arrow Sewer & Drain provides sewer leak detection and repair across central New Jersey, with primary service in Middlesex, Somerset, Union, Monmouth, and Hunterdon counties.
Signs of a Sewer Line Leak
Sewer leaks rarely produce a single dramatic symptom. They produce a pattern of small ones, and the pattern matters more than any one item on the list. A single slow drain is not a leak signal. A slow drain plus a sewage smell in the basement plus a green stripe across the lawn — that is a pattern, and it’s worth a camera.
The signs tend to fall into four groups, and what group a sign belongs to tells you something about where the leak probably is.
Signs you can see on the surface. A wet, soft, or unusually green patch of lawn that follows the path of the sewer line — typically running from the house out toward the street — is one of the most reliable above-ground indicators. Wastewater is rich in nitrogen, and grass directly above a leak grows faster, thicker, and greener than the surrounding lawn. In dry summer stretches, you’ll often see a clear stripe of healthier grass tracing the line. Pavement settling, cracking, or developing a low spot along the same path is the same signal at a more advanced stage — the soil under the pavement has washed out where the pipe is leaking.
Signs inside the home. A persistent sewage or sulfur smell in the basement that does not clear with cleaning is the most common indoor signal. Sewer gas is supposed to stay in the pipe; when you can smell it, the pipe is not sealed somewhere. Water damage, dampness, or unexplained moisture on basement walls or floors near where the sewer line exits the foundation points to the same thing closer to the house. Mold or mildew growing in spots that have no obvious water source is sometimes a sewer leak that has been working quietly for a while.
Signs in plumbing behavior. Gurgling from toilets when other fixtures drain, slow drains across multiple fixtures, and recurring backups that come back even after professional drain cleaning all point to something restricting flow in the main line. Roots growing through a leak are the most common reason — see root intrusion in NJ sewer lines for the longer version of that story — but partial collapses and bellies produce similar symptoms.
Signs in the bills and around the property. A sudden jump in your water bill with no explanation can point to a leak on the water service line (the pipe bringing potable water in). Sewer leaks themselves do not show up on the water bill, but the conditions that produce one often coincide with a service-line problem on the same property. A sudden uptick in flies, ants, or rodents around a particular section of foundation or yard is a less obvious signal — leaks attract pests, and sustained pest activity in a specific spot is sometimes the first thing a homeowner notices.
None of these symptoms is a diagnosis. Each one tells you something is worth checking. The diagnosis comes from running a camera through the line.
What “Leak Detection” Actually Involves
When a homeowner calls a contractor for leak detection, the work that follows depends on what the symptoms suggest and what equipment the contractor brings. There isn’t a single “leak detection method” there is a sequence of techniques, each suited to a different situation.
Camera inspection. For a sewer line, this is the foundation of any honest leak-detection work. A waterproof camera on a flexible push rod is fed through the line from a cleanout (or a pulled toilet if there’s no cleanout) and produces continuous video of the pipe’s interior. The camera shows breaks, cracks, separated joints, root intrusion, and bellies that pool water — the whole inventory of what could be producing a leak. Modern push cameras include footage counters and locator transmitters, so the exact distance and depth of any defect can be marked at the surface. Without this step, anyone telling you they’ve “detected” a leak is guessing about its location and cause. A more complete walkthrough of what a camera shows is in our guide on what cameras actually show.
Electronic line locating. The locator transmitter at the camera head pairs with a handheld receiver above ground. Once a defect is identified on camera, the technician walks the surface with the receiver until it pinpoints exactly where the camera is — usually within an inch or two horizontally and accurate to depth as well. This is what turns “there’s a leak somewhere in your line” into “the leak is 32 feet from the cleanout, 4 feet down, under the edge of the driveway.” That distinction is the difference between a targeted spot repair and a full line replacement.
Acoustic leak detection with geophones. A geophone is a sensitive ground microphone that picks up the sound of water or wastewater escaping from a pressurized or partially pressurized line. The technician moves the geophone along the surface above the suspected leak path, listening to the characteristic hiss or rush of escaping fluid. Geophones are most useful when a leak is suspected but has not shown clearly on camera — a hairline crack that opens only under flow, a leak below the camera’s waterline, or a pressurized water service line where camera inspection isn’t an option. They are also useful for narrowing down a leak location quickly before bringing in heavier equipment, particularly under hardscape where exposing the pipe is expensive. Skilled use matters here — distinguishing the sound of a leak from background noise, traffic vibration, or flow through nearby pipes takes training.
Hydrostatic and pressure testing. Used more often for water service lines than sewer lines. The line is isolated and pressurized; a pressure drop confirms a leak exists, even if the camera footage is ambiguous. For sewer lines specifically, hydrostatic testing is usually reserved for cases where the leak is suspected but not visible on camera — a hairline crack that doesn’t show clearly, or a leak below the waterline of a partially full pipe. Often paired with geophone work to pinpoint where the leak the pressure test confirmed is.
Smoke testing. Non-toxic smoke is forced into the line, and the technician watches for smoke escaping at the surface or through cracks in basement walls, foundation seams, or the ground above the pipe path. More common in commercial and municipal work than residential, but useful when a sewer gas smell is intermittent and a camera has not found an obvious source.
Dye testing. Colored dye is added to the line and the technician watches for it surfacing somewhere it should not — in a yard, a stream, or a separate drainage system. Mostly used to confirm a suspected leak path or to determine whether two pipes are connected when records are unclear.
Hydro-excavation for verification. When the camera flags a problem outside the pipe wall — a belly, a settled section, a separated joint without a clear cause in the pipe — pressurized water and a vacuum can selectively expose the pipe and surrounding soil at the specific section flagged on camera, without a full open trench. Once the bedding is visible, the actual condition can be assessed directly. This isn’t always part of leak detection, but when the camera tells you the problem is on the soil side of the pipe wall, hydro-excavation is how you confirm what’s actually happening before deciding on a repair.
The right combination depends on what the symptoms suggest. For a typical residential sewer line with a recurring backup or a green stripe in the yard, the answer is almost always camera inspection plus locator data. For a sewer gas smell with no other symptoms, smoke testing might be added. For a service-line leak suspected from a water bill spike, pressure testing plus geophone work usually leads. A contractor who only offers one method and tries to fit every situation to it is a contractor whose toolkit is shaping their diagnosis.
What Detection Doesn’t Tell You
Finding where a leak is doesn’t tell you why the pipe is leaking. That distinction is the part most leak-detection conversations skip, and it’s the part that determines whether a repair will hold.
A leak through a corroded section of cast iron is a different problem than a leak at a joint that pulled apart because the soil under it shifted. The first is a pipe-side failure — the pipe wall failed and the fix is replacing or lining the pipe. The second is a substrate-side failure — the bedding moved and dragged the pipe with it, and lining or replacing the pipe in the same conditions sets up the same failure on the same timeline. We cover this distinction in detail in why sewer lines fail, because it changes the right repair more than almost any other variable.
For leak detection specifically, the practical implication is this: a contractor who pinpoints the leak and immediately recommends a repair without addressing why the pipe failed there is solving half the problem. The honest next question after “where is the leak” is “what’s the camera telling us about the condition around the pipe at that spot.” Sometimes the answer is “nothing — it’s a clean pipe-side defect, here’s the targeted repair.” Sometimes it’s “the pipe is fine but the bedding has moved, and we need to physically verify the soil before we recommend a method.” Both answers are legitimate. A contractor who only ever gives the first one isn’t reading the camera fully.
What Happens After a Leak Is Found
Once detection has identified where the leak is and what kind of failure produced it, the repair options sort into a few familiar categories.
For an isolated pipe-side defect on otherwise sound pipe — a single cracked section, a separated joint without underlying soil movement, root intrusion at one spot — a trenchless spot repair often handles it in a single visit without a full excavation. For broader pipe-side deterioration along a longer run — multiple cracks, deteriorated Orangeburg, root intrusion at several joints — cured-in-place pipe lining creates a new structural pipe inside the old one and eliminates the joints that produced the leaks. For severe pipe failure or undersized lines that need upsizing, pipe bursting replaces the pipe entirely with seamless HDPE through a path the old pipe occupied
When the failure is substrate-driven — when the leak exists because the soil around the pipe moved — trenchless methods don’t fix the underlying problem. The repair in that case is excavation: removing the failed soil, replacing the bedding with proper material, and re-laying the pipe at correct slope. It’s more invasive and more expensive, but it’s the only repair that addresses why the leak happened. A trenchless repair on a substrate-driven failure usually fails again on a similar timeline. For more on what drives the cost difference between these methods, see why sewer line replacement is so expensive.
If you’ve already received a repair quote and the contractor’s recommendation seems to skip past the why, what to look for in a sewer line replacement quote walks through what a complete quote should specify, and a free second opinion from a different contractor costs nothing.
How This Differs for Commercial Properties and Municipal Sewer Mains
The detection methods covered above are the same toolkit used across residential, commercial, and municipal work — but the symptoms that bring someone to call, the equipment scaled to the job, and the urgency thresholds shift meaningfully depending on what kind of system is failing.
Commercial properties. The lateral serving a commercial building — a restaurant, retail center, office, or multifamily property — carries heavier loading than a residential line: more fixtures contributing simultaneously, grease and solids from food service, and often a longer run from building to municipal connection. The symptoms shift accordingly. Recurring backups that return shortly after jetting usually point to grease accumulation, root intrusion at multiple joints, or a structural defect a snake can’t address. Slab leaks under commercial kitchens, soft spots or settling in parking lots above the line, and odors at floor drains that don’t clear with trap-priming are the commercial equivalents of the residential signals above. Detection on commercial work typically uses larger-diameter cameras with stronger lighting, more aggressive pre-inspection jetting to clear grease and solids, and more attention to the grease interceptor and its discharge line as part of the system. The urgency calculation is also different — a backup at a restaurant during service or at a multifamily building affecting multiple tenants is an immediate-response situation regardless of how the symptoms would be classified at a single-family home.
Municipal sewer mains. A failing sewer main in the public right-of-way produces a different set of signals entirely, because the failure is happening below a roadway rather than a yard. Sinkholes or depressions in the pavement along the line alignment, sewage surfacing through cracks in the road, multiple connected properties on the same block experiencing backups simultaneously, and persistent odors at manholes or curb inlets are the characteristic warnings. Detection scales up accordingly. Push cameras give way to crawler-tractor CCTV systems for larger-diameter mains, capable of producing the standardized condition reports municipalities use for asset management and capital planning. Smoke testing is more common at this scale, both for locating cross-connections with storm sewers and for identifying defects across long runs efficiently. Flow monitoring and infiltration-and-inflow studies sometimes precede leak detection on municipal systems, because the question is often not just “is there a leak” but “where is groundwater entering the system and how much treatment capacity is it consuming.” The repair decisions that follow — full replacement, cured-in-place lining at scale, point repairs coordinated with paving cycles — are governed by capital budgets and inspection-report priorities rather than the homeowner-scale calculus covered above.
The underlying logic is the same across all three contexts: pattern of symptoms, camera-led diagnosis, distinguishing pipe-side failures from substrate-side failures and matching the repair to what the inspection shows. What changes is the scale of the equipment, the standards the report must meet, and how the urgency is calculated.
Arrow Sewer & Drain provides leak detection and repair for residential, commercial, and municipal systems across central New Jersey, including CCTV inspection, hydro-excavation, trenchless lining and bursting, and full-scale excavation for substrate-driven failures.
When to Call Right Away vs. When to Schedule
Not every leak signal needs a same-day call. Some do.
Call immediately if: sewage is backing up into the basement, you’re smelling sewer gas indoors (not just outside near the line), water is visibly pooling in the basement near where the sewer exits the foundation, or pavement is sinking suddenly along the line path. These are signs the line has progressed past slow leaking into active failure, and the longer they continue, the more damage stacks up — to the pipe, to the soil supporting it, and potentially to your foundation.
Schedule an inspection in the next week or two if: you have a green stripe across the lawn, a faint sewage smell outdoors, recurring slow drains that don’t clear with normal maintenance, or gurgling that’s been getting worse over time. These are early-to-mid-stage signals. They’re not emergencies, but they don’t get better on their own — and catching them now means more repair options and lower costs than catching them after they have progressed.
Get a baseline inspection if: your home was built before 1972, you have mature trees along the sewer line path, or you’re planning a renovation that will tie into the existing system. None of those is a symptom, but each one is a strong predictor that the line has problems waiting to be found. A camera inspection now beats discovering them through a basement backup later.
Where to Go from Here
If you are seeing signs of a sewer leak and you haven’t had a camera through the line yet, that’s the right next step — not a repair quote. A proper inspection will tell you whether you have a leak, where it is, and what kind of failure produced it. Everything that comes after — the repair recommendation, the method choice, the cost — should reference what the camera shows.
Arrow Sewer & Drain provides camera inspection, leak detection, and sewer repair across New Jersey for residential, commercial, and municipal systems, with primary service in Middlesex, Somerset, Union, Monmouth, and Hunterdon counties. If you have already had an inspection elsewhere and want a second opinion on what was found or what was quoted, contact us — that costs you nothing and frequently changes the conversation.
Contact Arrow Sewer & Drain for sewer leak detection and repair across central New Jersey.
