Leak under the kitchen sink
First find out when it leaks. Only when water runs or drains means the waste side. All the time, taps off, means the pipes under pressure.
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Empty the cupboard and dry everything
Take everything out, dry every pipe, hose and joint with kitchen roll, and lay dry paper on the cupboard floor so a new drip shows straight away.
Does the sink leak only when the tap runs?
This one check splits the cupboard in half.
- Leaks only when water runs or drains: it is on the waste side, the plughole seal or the trap and its joints. Fill the sink, pull the plug and watch the waste with a torch.
- Leaks with the taps off: it is on the pressure side, the tap hoses, the isolation valves, or the pipes coming up through the floor. Wrap dry tissue round each joint and leave it for an hour.
A split recommended in trade guidance, for example Checkatrade: leak under the kitchen sink.
The stop tap is here too
In most homes the internal stop tap sits under the kitchen sink. It can drip from its spindle. It is also the tap you close for the meter test on the home page.
Parts that leak under a kitchen sink
The numbers match the drawing.
| Part | How it shows | Who fixes it |
|---|---|---|
| 1Tap hoses and isolation valves | Wet all the time, taps on or off. Look for rust on the braiding or a damp valve. | You or a plumber |
| 2Plughole seal | Drips from under the plughole when the sink is full or draining. | Plumber |
| 3Trap and waste joints | Drips from a nut or bend when water drains, often worse with a full sink or the dishwasher emptying. | You or a plumber |
| 4Stop tap | A slow weep from the spindle, sometimes only after the tap has been turned. | Plumber |
When the water comes from somewhere else
Water finds the lowest point, and the sink cupboard often is one. A dishwasher or washing machine next door, a pipe running behind the units, or a leak under a solid kitchen floor can all end up in the cupboard.
If every joint stays dry through both checks, read your water meter with everything off. If it moves, water is escaping from a pipe you cannot see, and the leak finder helps narrow it down.
Cupboard dry, floor still wet?
If everything under the sink stays dry and the kitchen floor still gets wet, the water is coming from a pipe under the floor or behind the units. ADI traces it and marks the leak on site before any repair is discussed.
- 25 leak investigation engineers, around 5,000 jobs a year across England, Scotland and Wales
- A fixed price quoted before you book, and a written report you can give your insurer
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ADI figures as of September 2026, from ADI's About page. Trustpilot rating read 28 September 2026.
Kitchen sink leak questions
What should I do when water leaks from under the kitchen sink?
Empty the cupboard, dry everything with kitchen roll, and put a dry towel or paper on the cupboard floor. Then run the checks on this page: first whether it leaks only when water runs, then which joint gets wet. If it is more than a drip, close the stop tap, which in most homes is in this cupboard.
Is a leak under the sink an emergency?
A drip from the waste that only happens when the sink drains can wait for a plumber if you avoid using the sink. A leak that keeps going with the taps off is under mains pressure, so it will not stop on its own: close the isolation valve or the stop tap and get it fixed soon.
How much does it cost to fix a leaking pipe under a sink?
Tightening a trap nut or replacing a tap hose is usually quick, and often DIY. A new plughole seal takes longer because the waste has to come apart. A leak on a pipe coming up through the floor needs finding first.
This site does not publish prices.
How can I fix a leak under my kitchen sink?
Hand tighten plastic trap nuts first. A waste leak is often a nut that has worked loose or a washer that has slipped. For tap hoses and isolation valves, turn the water off before touching them and replace a hose that is kinked, rusty or bulging. If the sink edge or plughole leaks, the seal needs remaking.