Exfiltration is the sewer problem nobody sees. Water and sewage leave the pipe through a joint or a crack, soak into the soil, and the pipe keeps working as if nothing were wrong. A camera inspection looks at the inside of the pipe wall, and a joint that leaks outward can look perfectly ordinary from inside because the gap is on the far side of the wall or is covered by a thin film of flow. That is why a sewer camera, which is the right tool for almost every other lateral problem, is only part of the answer for this one.
Quick answer: exfiltration rarely shows directly on camera. What shows are its consequences: a joint with a dark gap, a stain or scour mark on the wall at a joint, a void or soil visible behind an opening, settlement or an offset downstream of the leak, and in wet weather the same joint leaking inward. A camera inspection should flag those joints as suspect; a hydrostatic test, a dye test or a smoke test is what confirms the leak. Lining seals every joint at once and is the usual repair.
Why the camera misses it
Three reasons. The leak path is outward, so from inside the pipe the joint may show only a hairline. Flow covers the invert, where most leaks are, with a film of water that hides the gap. And the camera is moving; a joint that drips a little between uses gives no sign while the head is passing at walking pace. A camera can also be fooled by a joint that is dry inside because the leak has carried the water away, which is the opposite of what intuition expects. Our guide on what a sewer camera cannot detect puts exfiltration at the top of the list for exactly these reasons.
The indirect signs to look for
A joint with a visible crescent of gap, even a small one, is a leak candidate. A clean, scoured patch of wall at a joint means water has been moving across it. A dark stain or a white mineral deposit at a joint means water has been evaporating there. Soil, gravel or a black void visible through any opening means the bedding has been washed away by water leaving the pipe. An offset or a belly just downstream of a suspect joint often means the leak undermined the next section. And in wet weather the same joint may leak inward, which is the reverse of the same defect; the infiltration guide covers that side. Slow down at every joint, dim the LEDs, and record the counter reading at each suspect.
Why exfiltration matters
For the pipe, it means soil loss, settlement, offsets and eventually separation, the same chain of events as infiltration run backward. For the property, it means sewage in the soil beside the foundation, under a slab or in a crawlspace, which brings odour, damp and in some soils a sinkhole. For a well-and-septic property it is a contamination route. And for a sale it is the finding that a buyer’s inspector raises and a seller’s camera inspection did not show, which is why a camera report that says “no defects observed” is honest and a report that says “no leaks” is not. The limits every customer should know apply here.
The tests that find the leak
A hydrostatic test plugs the line, fills it with water to a set level and watches whether the level drops; it proves a leak exists and how fast, without saying where. A dye test adds dye to the flow and looks for it in the soil, a sump, a crawlspace or a neighbouring drain. A smoke test blows smoke into the line and looks for it escaping at the surface, which finds cracks and open joints quickly on a dry day. None of them replaces the camera, which is what finds the suspect joints to test, and the camera does not replace them. Sewer camera vs hydrostatic test compares the two in detail.
What to do about a leaking lateral
If the camera and a test agree that joints are leaking and the pipe is otherwise sound and round, lining seals every joint in one operation and is the standard repair. If a single joint is leaking badly with a void behind it, a spot repair with the void filled is the answer. If the pipe is channeled, fractured or collapsed, replacement. In every case a camera pass after the repair confirms the joints are sealed, and a second test, if one was done before, provides the proof. CIPP lining explained covers what the camera checks before and after a liner.
Recording suspect joints
Note the counter reading at every joint that shows a gap, a scour mark or a stain, and say in the report that these are suspect joints rather than confirmed leaks. A later test can then be aimed at the right section of pipe instead of the whole lateral.
Common questions
Can a sewer camera find a leak?
It can find the joints most likely to be leaking and the damage a leak has caused. It cannot usually see sewage leaving the pipe.
Is a dry joint on camera a sound joint?
Not necessarily. A joint can be dry inside because water is leaving through it. Look for scour marks and gaps.
What test confirms exfiltration?
A hydrostatic test proves the line loses water. A dye or smoke test shows where. The camera then narrows it to a joint.
Related guides
See offset joints on camera, holes and voids on camera, and the best sewer cameras for residential inspection.