The core idea
Pressurized supply leaks and gravity drain leaks often differ in timing, persistence and relationship to fixture use.
How the mechanism works
Supply lines can leak whenever pressurized, while drains usually leak only when water passes through a defective joint or fitting.
When it becomes relevant
Typical trigger: Continuous pressure, specific fixture use or appliance cycles.
Evidence that supports this interpretation
- Wetness continues with no drainage use
- A specific discharge cycle reproduces the symptom
- Meter or isolation evidence supports one side
Evidence that weakens it
- No plumbing route exists
- Rain is the stronger trigger
- Condensation explains the location
What this concept cannot prove alone
A single observation, image or meter reading cannot confirm the complete failure pathway. Use this concept to form better questions, compare alternatives and decide which safe observation would be most informative next.
Safety and professional boundary
Do not open pressurized systems, ceilings near electricity or contaminated drains without qualified help.
Primary references for this topic family
These references ground the general building-science or safety context. They do not diagnose a specific house, replace local requirements or certify a repair.
