This is different from a ceiling that is actively dripping. A stain proves that moisture was present; it does not prove the source is still active.
Match the stain to timing
Growth after rain makes roofing, flashing, skylights, and chimneys more likely. A stain that changes after showers, laundry, or use of an upstairs bathroom points more toward plumbing.
The visible spot may not be below the entry point
Water can travel along framing before reaching drywall. Repairing directly above the stain without tracing the path may miss the source entirely.
Find out whether the assembly is actually dry
A surface can feel dry while material behind it remains damp. Musty odor, bubbling paint, soft drywall, or visible growth needs further investigation.
Condensation can stain too
Cold ducts, missing insulation, or high indoor humidity can create recurring droplets without a broken pipe. A seasonal pattern can help separate condensation from a leak.
Do not paint until source and drying are resolved
Stain-blocking primer hides color, not moisture. If the area is large, the ceiling is sagging, or electricity is involved, stay clear of the area and get qualified help.
Take dated photos. A stain that changes over time provides far more diagnostic information than its color alone.
Sources
- U.S. Environmental Protection Agency — A Brief Guide to Mold, Moisture and Your Home — Moisture control, drying, mold prevention, and when water damage needs broader remediation.