Leaking pipe under the sink?

The cupboard under the sink smells damp, the base is swollen, or there's a puddle every morning. A leak under the sink is one of the most common things we fix, and it's often a loose joint you can tighten yourself.

Is it the waste or the supply?

• Only leaks when you use the sink or empty a bowl: it's the waste side. The trap (U-bend), the waste pipe or the plughole seal.
• Leaks or drips all the time, even with the taps off: it's the supply side. A hot or cold pipe, a joint, a flexible tap connector or an isolation valve. This is under mains pressure, so deal with it quickly.

Dry everything with a towel, put a sheet of kitchen roll underneath, then run the tap and watch where the first drop appears.

Fixing a waste leak

1. Put a bowl under the trap.
2. Unscrew the trap by hand, check the rubber washers inside each nut are seated and not split, then screw it back on firmly by hand. Plastic waste fittings shouldn't be tightened with tools.
3. If the leak is where the plughole meets the sink, the seal under the plughole may need redoing.

Fixing a supply leak

1. Turn off the water. Use the small isolation valve on the pipe (turn the slot across the pipe) or the main stopcock.
2. Compression joint dripping: a quarter turn of the nut with a spanner often stops it. Don't overtighten, as it can split the fitting.
3. Flexible tap connector wet or bulging: replace it. These braided hoses can burst without warning, so don't leave a damaged one in place.
4. Dishwasher or washing machine connection: check the hose washer and that the hose is screwed on fully.

When to call a plumber

Call us if water is spraying, you can't turn it off, the pipe itself is corroded or cracked, or it still leaks after tightening. If the cupboard base and floor are soaked, check that water hasn't reached any sockets behind the units. If it has, switch off at the fuse box. For a pipe that has burst, see burst pipe repair.

Common questions

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