Water coming through the ceiling — what should you do?

Ceilings contain light fittings, and water finds them. If water is coming through near a light, a downlight or a ceiling rose, or running down a wall towards sockets, isolate the electricity to that area at the consumer unit.

Only do this if you can reach the consumer unit without standing in water or reaching through a leak. If you cannot, keep everyone away from that part of the property and call an electrician or your supply emergency number.

A bulge in a plasterboard or lath-and-plaster ceiling means water has pooled above it. Saturated plasterboard becomes very heavy and can fail suddenly and completely.

• Clear the room of people and pets and keep the door shut
• Move furniture and belongings out only if you can do so from the edges of the room, safely
• Do not poke, prod or 'release' a bulging ceiling unless you know what is above it and have somewhere for the water to go
• If a large area is sagging, treat the room as out of use until it has been looked at

Water travels along joists and can appear several metres from where it entered, so the wet patch is not necessarily below the leak. Common sources, roughly in order of how often we see them:

• Bathroom above — a leaking shower tray, failed sealant, an overflowing bath or a waste pipe joint
• Concealed pipework in the floor above, including heating pipes
• A loft tank, overflow or a failed connection in the loft
• A washing machine or dishwasher on the floor above
• A radiator valve or heating pipe connection
• Roof water entering the loft and running along the structure before it drops through

If the water is clean and pressurised, turn off the stopcock. If it appears when someone uses a shower or bath, stop using that room. If it follows rainfall, the source is likely to be the roof or external fabric rather than plumbing.

Buckets and towels are unglamorous but effective. Put down a bucket with a towel in it to stop splashing, protect the floor around it, and lift anything absorbent out of the way. Empty containers before they overflow — a slow drip becomes a lot of water overnight.

What you can see is the underside of the ceiling. What matters is the space above it — joists, the top of the plasterboard, and very often insulation, which soaks up water and holds it against timber in an unventilated space.

Wiping the ceiling and repainting it does nothing for that. Wet insulation left in place keeps releasing moisture for weeks, produces a musty smell, and creates conditions where mould develops out of sight. Drying a ceiling generally means getting access to the void, removing insulation that will not dry in place, and drying the structure with controlled airflow and dehumidification.

• An electrician, if water has reached lighting, sockets or the consumer unit
• A plumber, to find and repair the source of the leak
• Your insurer, if you think you may claim — early is usually better
• A drying specialist, to establish how far the water has spread and dry the structure

If you are in a flat and the water is coming from the property above, contact the occupier or the managing agent as soon as you can — the source has to be stopped from their side.