Water Dripping From the Ceiling Below a Bathroom

A damp patch on the ceiling directly below a bathroom is the single most common leak complaint in Indian flats — and the most commonly misdiagnosed. The usual response is to reseal the bathroom floor. That fixes one of the four causes. If yours is one of the other three, you will have paid for the work and the ceiling will still be wet.

The four causes

1. The floor waterproofing has failed

Water passing through the tile joints reaches a floor membrane that has cracked, was never laid, or stops short of the walls. It travels sideways in the screed and appears on the ceiling below, often some distance from the bathroom itself.

Tell-tale: the patch is broad, diffuse, and worst after long use — a wash day, guests staying. It dries slowly over days.

2. A supply pipe is leaking

A pressurised line inside the wall or floor. This leaks whether or not anyone is using the bathroom, because the pipe is under pressure day and night.

Tell-tale: the patch never fully dries, even when the bathroom is locked and unused. This is the decisive test and it costs nothing — keep the bathroom completely dry for two or three days and watch the ceiling. Still wet, still growing? It is a supply pipe.

3. A waste or drain pipe is leaking

A cracked joint on the outlet from the WC, basin or floor trap. Unpressurised, so it only leaks when something drains through it.

Tell-tale: the patch darkens shortly after the bathroom is used and fades between uses. Often smells. Frequently accompanied by staining that follows the pipe run rather than spreading in a circle.

4. The wall-floor junction, not the floor

The membrane covers the floor but was not turned up the wall, or was turned up and then cut through when the wall tiles were fixed. Shower water runs down the wall, reaches the junction, and passes behind the membrane instead of over it.

Tell-tale: the ceiling patch sits under the shower corner specifically, not under the middle of the room.

Working through it in order

Dry test. Bathroom unused for two to three days. Ceiling still wetting = supply pipe. Ceiling dries = go on.
Fixture test. Use one fixture at a time on separate days — only the WC, then only the basin, then only the shower. Which one wakes the patch tells you which line or which zone.
Flood test. Block the floor trap, hold 25–50 mm of water on the floor for a few hours, and watch. Patch appears with no fixture running = the floor itself.
Map it. Mark the wet edge on the ceiling with pencil each day. A patch that grows steadily is active; one that stays put is historic and may already be repaired.

These four steps cost nothing but patience, and they are the difference between one targeted repair and three speculative ones.

What each cause actually needs

Supply pipe — the pipe replaced or rerouted. No coating fixes a pressurised leak. Waterproofing the floor afterwards does not address it.
Waste pipe — the joint remade. Usually a small opening in one place.
Floor membrane — the floor stripped and rewaterproofed properly. See bathroom waterproofing for what a correct job includes.
Wall junction — the coving and the first 300 mm of wall redone, membrane turned up and lapped. Often the cheapest of the four.

The ceiling itself

Repair the source first. Treating the ceiling while the leak is live wastes the material — new putty and paint on a wet slab will blister within weeks. Once the source is fixed and the slab has dried out fully, scrape back to sound plaster, let it dry, and finish. If salt deposits have appeared, read efflorescence on walls before repainting.

When the bathroom belongs to someone else

In a flat, the leak is usually in the unit above. That is a conversation, not a repair — and it goes better with evidence. The dry test and the fixture test give you something concrete to show: not "your bathroom is leaking" but "the patch grows only when your shower runs". Do the tests before you knock on the door.