Two sewer videos recorded a few months apart do not necessarily show deterioration. A crack may become visible because a deposit has been removed; an area may look larger because the camera moves closer. Comparing inspections starts with establishing that you are looking at the same location under sufficiently comparable conditions.
For an owner of a house, plex or small building in Laval, the practical goal is to understand what changed before deciding on follow-up. This guide focuses on comparisons between two dates. It does not replace technical interpretation of the images or an assessment of what caused damage.
Key takeaways
- A newly visible anomaly did not necessarily appear after the first video.
- Dates, routes and reference points must allow the same sections to be matched.
- A clearer image changes the quality of the observation, without necessarily indicating a change in the pipe.
- A conclusion about progression should explain the observed change and the limits of the comparison.
Table of contents
- Define what the two videos need to compare
- Match the same reference points first
- Distinguish an exposed surface from new damage
- Recognize differences created by the images
- Build a useful comparison file
- Request a conclusion that explains the change
- Frequently asked questions
- Keep a reference for the next decision
Define what the two videos need to compare
Start with a specific question. Do you want to know whether an opening looks different, whether a deposit is returning or whether the repaired section matches the one previously identified? These questions do not all require the same images. A summary stating that “the sewer is worse” is too vague to organize a useful comparison.
CERIU describes video inspection as a way to track a pipe’s interior condition over time (French). However, that follow-up requires observations that can be matched. Two recordings do not automatically have the same comparative value simply because they relate to the same property.
The first video might show the house sewer connection and the second another line accessible from the yard. The file name, customer address or appearance of the same equipment does not establish that the routes are identical. Ask which line and which section each document actually covers.
Separate physical condition from performance, too. Better drainage after an intervention does not, by itself, answer whether a crack has changed. Conversely, a pipe wall that looks similar does not necessarily explain a change in performance. Record the two questions separately so that a favourable answer to one is not used to draw a conclusion about the other.
The drain camera inspection service explains the general scope of the examination. The additional task here is to compare two identifiable observations, rather than repeat the entire interpretation of a single recording. Defining that purpose first helps you request the right sequences and commentary.
Name the change you are investigating
Write a neutral sentence: “check whether the joint near the change in pipe material has the same appearance.” Avoid starting with “prove that cleaning broke the pipe.” The first wording opens a question; the second already assumes an outcome and a responsibility that a visual comparison cannot establish on its own.
Number the questions if there is more than one. A changing deposit, a newly exposed wall surface and a recent repair may call for three separate comparisons. Keeping them separate prevents one unsettling still image from becoming a verdict on the entire system.
Match the same reference points first
Ask where each inspection started and which direction the camera travelled. If the second camera enters from the opposite end, the sequence of joints and branches will be reversed. Scenes cannot therefore be matched simply because they occur at the same number of seconds in each file.
Playback time identifies a moment in the recording, rather than a fixed location in the pipe. Pauses, reverse movements and different travel speeds make second-by-second comparisons misleading. A twenty-second clip might cover a short, detailed observation or a much longer movement through the line.
The distance shown on screen also needs context. Ask where its starting reference is and which unit it uses. The same number on two screens does not necessarily identify the same joint when the starting point or route differs. The goal is an explained match supported by recognizable landmarks, without treating the display as an absolute measurement.
A change in pipe material, a distinctive series of joints or an identifiable connection can help the professional establish that match. Keep some footage before and after the anomaly. Two isolated close-ups remove the very features that help establish where the camera is.
In its explanation of assessment protocols, CERIU describes the value of consistently recorded observations for tracking deterioration (French). That principle helps organize residential documents. It does not mean every owner needs a municipal database, or establish that any particular company holds a certification.
When the match remains uncertain
Write “same section to be confirmed” rather than selecting the most dramatic pairing. Ask what information would resolve the uncertainty: a longer sequence, the initial report or confirmation of the access point used. A comparison with an uncertain location should not become evidence of progression.
If one inspection stopped before reaching the area, refer to the guide on a drain camera that cannot advance. A section missing from the first examination provides no reference image, even when the rest of that recording looks reassuring.
Distinguish an exposed surface from new damage
Reconstruct the work performed between the two dates before attributing a difference to deterioration. Was there cleaning, emergency clearing or a repair? Do you have only two videos, or also a report describing the conditions of each inspection? Those details affect what it is reasonable to ask the images to establish.
Consider a fictional example: the first sequence shows an opaque layer covering part of the wall. After work is performed, the second shows a dark line in that area. You can say that the line is now visible. To say it appeared between the two dates, the first observation would need to provide an actual view of that surface.
“Nothing was noted in the first report” does not replace that check. It may mean no anomaly was recorded, but it does not establish that every detail visible today could be observed then. Ask which part of the first video supports the comparison, rather than inferring its contents from the summary alone.
The CERIU technical guide published in February 2018 (French), in its quality-control sections, explains that deposits can limit analysis and that camera position, lighting and image clarity affect interpretation. Those observation principles are useful here; municipal network inspection requirements do not thereby become identical obligations for a residential assignment.
The reasoning works in the other direction as well. An area hidden in the second video does not establish that a previously visible defect has disappeared. “Not identifiable on this pass” is different from “corrected.” The report should preserve that distinction.
Do not confuse deposit removal with repair
Footage showing less material can document a change in visibility or obstruction. It does not automatically demonstrate that a joint has been made watertight. For the specific question of roots returning after cleaning, our article about recurring root intrusion already explains the causes and options. The comparison simply needs to identify which phenomenon is being tracked.
Recognize differences created by the images
An enlarged screenshot on a phone and an overview on a computer can create very different impressions. Before calling a crack “twice as large,” ask how the images were obtained and whether a dimensional comparison is actually possible. The size displayed on a screen is not, by itself, a measurement of the defect.
Framing also changes the apparent importance of a detail. A pass close to the wall shows a small area more clearly; a more distant view provides greater context. Keep the originals instead of replacing them with cropped screenshots that no longer show their surroundings.
Orientation deserves the same attention. A camera can present the top, sides and bottom of a pipe differently. Do not try to recognize an anomaly solely from its position on screen. Ask the professional whether the two views actually show the same feature from a comparable angle.
Different brightness can give a line more contrast without demonstrating a change. Nor should you assume every dark line is a shadow. The useful response is to ask what the sequences allow the analyst to distinguish and what supports the identification being made.
Record difficulties rather than trying to remove them with filters. A brightened or heavily sharpened version may help discuss a detail, but it should not replace the file originally supplied. If someone prepares a comparison montage, keep the complete sequences as well and identify changes in presentation.
Different opinions do not establish different pipe conditions
The wording can change between two reports. One may describe a general observation while the other identifies it in greater detail. Ask whether the difference concerns the pipe, visibility or interpretation. More alarming terminology does not, by itself, establish physical deterioration between the two dates.
Build a useful comparison file
Create a separate folder for each inspection and one shared comparison document. Name files with the confirmed date and a short description of the route. If the date is uncertain, say so explicitly instead of using the download date as the date the work occurred.
Keep the original file, the associated report and documents describing work between the inspections. An invoice can help establish that cleaning took place; it does not necessarily describe the condition of every wall surface. Use each document for what it actually tells you.
Prepare a short record for each observation being compared:
- The question: what change are you trying to check?
- The match: which landmarks connect the two sequences?
- The first date: what detail is visible, and under what conditions?
- The second date: what does the same area show?
- The interval: which interventions are documented?
- The conclusion: observed change, different visibility or insufficient grounds for comparison?
Add useful playback times to help find the sequences, without presenting them as ground coordinates. In a plex, identify which line is involved and which access was used. The file should remain understandable to someone who was not present during the visits.
Identify missing information as missing. If you received only an excerpt from the first inspection, ask for the available document before filling gaps from memory. An old note remains useful, but it cannot replace a missing reference image.
The new specification guide announced by CERIU in 2025 (French) emphasizes quality inspections and reliable data for network management. For an owner, the file described above is a practical organization method, rather than an official form or a guarantee of diagnosis.
Request a conclusion that explains the change
A useful conclusion does more than recommend work. It answers the comparative question and shows the basis for that answer. Ask for a clear distinction between what is visible today, what was visible previously and the change that can reasonably be supported between the two.
Three statements can help clarify the degree of certainty: “the same feature appears on both passes,” “the area is now more clearly visible” or “the images do not support a reliable comparison.” These are practical discussion categories; they do not replace the professional’s technical terminology.
If progression is identified, ask which feature changed and how the observation conditions were taken into account. If progression cannot be established, ask what follow-up would be useful and what question it should resolve. Avoid ordering another video solely to obtain a different opinion without a defined purpose.
The date of a video identifies an observation, rather than necessarily the start of a defect. Similarly, a difference observed after work does not automatically identify its effect or who is responsible. Investigating a cause may require other information. Keep the documents and clarify that limit before drawing a conclusion about the timeline.
Finally, separate the current need from reconstructing the past. A situation requiring attention today does not become harmless because its age is unknown. Conversely, a stable appearance between two inspections is not a promise about future performance. Comparison improves the decision; it does not provide a guaranteed remaining service life.
Frequently asked questions
Is a crack newly mentioned in a report necessarily recent?
No. Check whether it is new in the wording or actually shown to have been absent before. A wall surface that was obscured or difficult to read on the first pass does not allow the appearance of a detail observed today to be dated.
Can videos from different companies be compared?
Yes, if the documents allow the same sections to be identified and the inspection conditions to be understood. Request an explained match between landmarks. Different companies do not make comparison impossible, or make the results automatically equivalent.
Is the same displayed distance enough to identify a defect?
No. You need to know the starting point, direction and route landmarks. Treat the displayed number as information to contextualize with the professional, rather than certain identification of a joint.
Does a post-cleaning video establish that cleaning caused damage?
The order of the dates does not establish the cause. A newly visible surface must be distinguished from an established change, and other information in the file considered. The images alone may leave that question unanswered.
Should images be modified to make comparison easier?
Always keep the originals. Annotated excerpts can help locate a detail, provided the complete sequences are retained and changes in framing or presentation are identified. An edited image should not become the only reference.
What if the first video is no longer available?
Look for the existing report, notes and work documents. They may clarify the history without recreating a lost image. The next examination can establish a new reference; it will not automatically recover the pipe’s exact condition on the first date.
Keep a reference for the next decision
Comparing sewer inspections takes more than placing two screenshots together. The question, shared landmarks, visibility conditions and intervening work all need to be understandable. A good comparison also identifies what it cannot establish.
Keep a written conclusion with the videos and excerpts supporting it. You will then have a useful history for the next follow-up, without confusing a new observation, a presentation difference and a demonstrated change in the pipe.
