Map the symptom
Record where staining or dampness appears, when it gets worse and what plumbing fixtures or pipe routes are nearby. Photographs over time are often more useful than a single image.
Test before opening where possible
Meter observations, isolation tests, moisture patterns and other diagnostic methods can narrow the likely source. The objective is to reduce unnecessary destructive opening.
Keep alternative causes open
Water can travel before it becomes visible. A wet wall may be caused by a supply leak, waste pipe, failed waterproofing, roof leak or external penetration. Diagnosis should not assume the first explanation is correct.
Related information
Leak Detection
Hidden leaks are best approached as a diagnosis problem. Start with evidence such as meter movement, pressure loss, damp patterns and the plumbing layout before opening finishes.
A Water Leak: What to Do in the First 30 Minutes
The first half hour is about safety, isolation, protecting contents and documenting the event.
Damp Wall Near Plumbing
Dampness near pipe routes can result from a concealed leak, waste leak, waterproofing failure, condensation or moisture from another source.
How to Use a Water Meter as a Leak Clue
A meter can show unexplained water use, but the result must be interpreted carefully before it is treated as proof of a concealed leak.