How do I stop a pipe leaking until a plumber arrives?

Temporary repairs that genuinely hold — a repair clamp, self-amalgamating tape, epoxy putty — and the order of actions that limits the damage while you wait.

Difficulty: beginner
Time: 20 min
Read: 5 min
Safety: warning

Short answer

Turn the water off at the stopcock, open a low tap to drain the pressure, contain the water, then apply a temporary repair: a proprietary pipe repair clamp is the strongest, self-amalgamating tape is the best improvised option, and epoxy putty works on a pinhole. All of these are temporary — the joint or pipe still needs replacing.

A leak at ten o'clock at night is a problem of containment rather than repair. The aim is not to fix it — a permanent repair means cutting out and remaking the joint, and that can wait for daylight. The aim is to stop the water, protect the building, and get through until morning. Everything here is temporary by design.

Safety

Water and electricity together are the real danger here, not the water itself. If water is running onto or near lighting, sockets, a consumer unit or any electrical accessory, switch off the affected circuits at the consumer unit before dealing with the water — and if the consumer unit itself is wet, do not touch it and call an electrician. Heating and hot water pipes carry scalding water; let them cool before working on them.

What you'll need

A pipe repair clamp or self-amalgamating tape
Epoxy putty (optional)
Cloths and a bucket
Emery cloth or a rag to dry the pipe
A torch

Step by step

Turn the water off.The internal stopcock for a mains leak. For a leak on tank-fed pipework, the stopcock will not stop it — tie up the ball valve in the loft cistern and close the gate valve on the affected feed. For a heating leak, switch the boiler off and close the valves either side of the leak if there are any.
Drain the pressure out.Open the lowest tap on the affected circuit and leave it open. Water in a pipe with the supply off is still under head pressure from anything above it, and a temporary repair applied to a pipe still under pressure will not stick.
Deal with the electrics.If water is running near or onto any electrical accessory, switch off the affected circuits at the consumer unit. If the consumer unit itself is wet, do not touch it, keep everyone away and call an electrician. This step comes before any repair.
Contain and protect.Buckets, towels and a plastic sheet. Move furniture and anything valuable. If water is in a ceiling and it is bulging, put a bucket underneath and make a small hole at the lowest point of the bulge to let it drain in a controlled way rather than the whole ceiling coming down.
Dry the pipe thoroughly.Every temporary repair needs a dry surface to work. Wipe the pipe, wait, wipe it again. A cold pipe in a damp cupboard keeps sweating — a hairdryer on a cool setting helps if there is a socket safely available.
Fit a pipe repair clamp if you have one.A proprietary clamp with a rubber liner, tightened over the leak with a screwdriver or a small spanner. This is by far the strongest temporary repair, holds full mains pressure, and takes two minutes. Worth keeping one of each common size with the household tools.
Use self-amalgamating tape as the improvised option.Stretch it hard as you wrap — it bonds to itself under tension, not by adhesive. Start well before the leak and finish well after, overlapping each turn by half its width, several layers deep. It is markedly better than any other tape for this and it costs very little.
Use epoxy putty on a pinhole.Knead the two parts together, press it firmly over a dry, roughened pipe surface and work it well beyond the hole in all directions. It needs time to cure before the water goes back on — read the pack, and allow longer than it says on a cold pipe.
Turn the water back on carefully, or leave it off.If you can manage overnight with the water off, that is the safest choice. If you must have water, open the stopcock slowly, watch the repair for several minutes, and know that it is temporary. Do not leave a temporary repair unattended overnight under full pressure if you can avoid it.

Tips

Buy a pipe repair clamp and a roll of self-amalgamating tape now and put them with the stopcock key. They cost very little and they are useless bought the morning after.
Photograph the leak before you cover it up. The plumber wants to see what it looked like, and insurers frequently ask.
Water tracks a long way along joists and pipes. The wet ceiling is rarely directly below the leak.
If you are on a water meter, note the reading before and after. A leak allowance claim is much easier with figures.

If it doesn't work

Leak from a compression joint rather than the pipe

Cause: A relaxed olive — Fix: Try a quarter turn on the nut with two spanners before anything else — it cures a large proportion of weeping joints outright and needs nothing else.

Pinhole in a copper pipe with a green stain around it

Cause: Pitting corrosion, common in some water areas and on pipes in contact with certain building materials — Fix: Epoxy putty or a clamp will hold it temporarily, but a pipe that has pinholed once usually pinholes again nearby. Plan to replace the length.

Split along a pipe rather than a hole

Cause: Freezing — water expanded and burst the pipe lengthways — Fix: A split is too long for putty. A clamp of the right length or heavy self-amalgamating tape may hold at low pressure, but a burst pipe needs a section cut out and replaced.

Leak on a plastic push-fit joint

Cause: Missing insert, pipe not pushed fully home, or a damaged O-ring — Fix: Turn the water off and try pushing the pipe fully home — many push-fit joints leak simply because they were never seated. Never try to tighten a push-fit joint.

Water coming through a ceiling with no visible pipe

Cause: The leak is somewhere along a run above and water is tracking — Fix: Turn the water off, contain and drain the ceiling. Do not start opening the ceiling in the dark — the water source is often a long way from where it appears.

Leak stops when the heating stops

Cause: A heating pipe or joint that only leaks when hot and expanded — Fix: Leave the heating off and use alternative heat until it can be repaired. Trying to seal a joint that moves with temperature rarely works.

Questions people ask

How long will a temporary repair last?

A proper repair clamp can hold for a long time, and they are used as semi-permanent repairs on some pipework. Tape and putty should be treated as days rather than months. None of them is a substitute for remaking the joint properly.

Should I turn the heating off too?

If the leak is on the heating circuit, yes. If it is on the water supply and you have turned the mains off, a combi will not be able to make hot water and should be switched off. On a stored system, switch the immersion off if the cylinder cannot refill.

Can I use gaffer tape?

It will not hold. Ordinary adhesive tapes fail immediately on a wet pipe under pressure. Self-amalgamating tape works because it fuses to itself rather than relying on adhesive, and that is the difference.