The first wet ceiling or wall is an observation point, not automatically the failure location.
DOWNTOWN SEATTLE / GUIDE
Read Water-Path Clues
Compare when evidence appears, which ordinary use precedes it, whether it travels, and what occupants above, below, or beside it observe.
PLUMBING ROUTE
Compare timing, direction, and elevation
Use elevation, direction, timing, fixture activity, weather, and adjacent-space reports without declaring a concealed source.
Supply, drainage, enclosure, roof, condensate, fire protection, and other building paths can overlap.
Leave overlapping building systems in view
Qualified access and testing are needed before a hidden route becomes a repair conclusion.