Look for a repeatable pattern
Note when a patch gets worse and whether the change follows rain, heating or use of a bathroom. Photograph the same area over time when safe. Check whether the problem is limited to a surface or appears in adjoining rooms.
Explain what has already been tried
If the area has been redecorated or treated for damp, keep the dates and any survey findings. A new finish can hide symptoms temporarily without resolving their source. Let the investigator know about recent plumbing or building alterations as well.
Match the evidence to the next trade
A plumbing leak investigation tests whether a water system is contributing to the problem. If the evidence indicates another cause, roof, building-fabric or ventilation expertise may be needed. The useful outcome is a reasoned next step, not an assumption that every damp patch needs a pipe repair.