Water in the cupboard under your sink? Find out if it is the waste, the tap connections or the sink seal, what you can tighten safely and when to call a plumber.
By AJ, certified Gas Safe engineer and lead plumber at 247 Emergency Plumbers Edinburgh · Checked
Most leaks under a sink come from three places: the waste trap and pipe, the tap supply connections, or the seal around the plughole. Dry everything, then run the tap and fill the sink in turn to see where the drip starts. If it is the supply pipes, turn off the small isolation valve or the stopcock first.
Water near electrics? Do not touch wet switches, sockets or light fittings. Switch off at the consumer unit only if you can reach it without standing in water. Water pouring in? Turn off the stopcock: find your stopcock →
What it could be and what to do
Only leaks when the sink drains You may be able to fix this
Likely cause: Sinks.co.uk says loose connections, a corroded trap or a blockage cause leaks at the waste trap.
What to do: Hand-tighten the plastic nuts on the trap. If it still drips, take the trap off over a bowl, clean it and refit it with the washers seated properly.
Leaks when the sink is full Engineer needed
Likely cause: Sinks.co.uk says if a leak appears when the sink is full of water, the plughole seal has probably failed.
What to do: The waste outlet needs resealing. Call a plumber if you are not confident.
Drips all the time Engineer needed
Likely cause: The tap supply pipes are under pressure all the time. Sinks.co.uk says loose compression fittings on the isolation valves are a common cause.
What to do: Turn off the isolation valve or stopcock. A gentle tighten of the nut, holding the valve with a second spanner, may stop it. Flexible tap connectors that are bulging or rusty should be replaced.
Water running down from the tap You may be able to fix this
Likely cause: Sinks.co.uk notes water can run down the back of the tap and drip underneath without being obvious.
What to do: Dry the base of the tap and watch it while it runs. A leaking tap usually needs a new washer or cartridge.
Safe checks you can do first
These are the checks we suggest before a plumber arrives. Stop if anything feels unsafe.
Stop the water: use the small isolation valve on the pipe to the fitting if there is one, or the main stopcock, usually under the kitchen sink. Stopcock finder →
Electrics: keep away from anything wet and electrical. Get an electrician to check before switching back on.
Is it just you? Ask neighbours. No water or brown water in the whole street is usually Scottish Water: 0800 0778 778, free, 24 hours.
Contain it: buckets, towels and moving belongings limit the damage. In a flat, warn the neighbour below.
Photos: take photos and video before you clear up, for your insurer or landlord.
Need a plumber now? Call us any time.
Our callout is from £75 in standard hours (out of hours £100–£180) for attendance and diagnosis. Any repair and parts are agreed with you before work starts.
Our emergency line is open 24 hours a day, 7 days a week.
Every property is different. This page is general guidance, not a diagnosis.
CLAIMING ON INSURANCE?
Trace and access, with a report for your insurer.
We find hidden leaks, open up only where needed, repair and make good, and give you a written report with photos and the cause. Insurer-referred jobs welcome.
Usually the waste trap, the tap supply connections or the plughole seal. Dry everything and run the tap, then fill the sink, to see when the drip starts.
Is a leak under the sink an emergency?
A steady drip from the supply pipes can soak the cupboard and floor quickly, and in flats it can come through the ceiling below. Turn off the isolation valve or stopcock and call us.
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