A stain or drip in the ceiling below a shower can come from the drain, a supply pipe, the valve, a tub joint, or the shower enclosure's waterproofing. Stop using the shower until the source is identified, especially when water is near lights or wiring.
Match the leak to exactly when it appears
If it leaks even when the shower is unused, suspect a supply line. If it appears only while draining, focus on the drain and overflow; if it depends on wetting walls or corners, waterproofing and joints become more likely.
Test in stages without flooding the area
With another person watching below and only when there is no electrical hazard, run a small amount of water directly into the drain without wetting walls. Then test specific areas; stop as soon as moisture appears to limit damage.
Do not patch the ceiling before fixing the source
Paint, filler, or caulk from below hides symptoms while wood, insulation, or gypsum may keep getting wet. Open finishes only when necessary for diagnosis or drying and after considering wiring and potentially hazardous materials in older buildings.
Water near electricity requires shutting power off from a dry location
Do not touch light fixtures, switches, or a saturated ceiling. If water reaches electrical components, turn off the circuit from a dry, safe panel if that can be done without approaching the wet area and call a professional.
Sources
- U.S. Environmental Protection Agency WaterSense — Home Maintenance — Household maintenance related to water, leaks, and efficient use.