EXPERT ADVICE
Leak under the kitchen sink? Here's what to do
Updated 07/26
By: Lara Sargent
Reviewed: Kim Staples
If you've found a leak under kitchen sink, it's important to get it fixed as soon as possible. Let our guide help you get to the root cause of the problem and what action you should take.
How to pinpoint exactly where a leak is coming from
The six most common causes of a leak under the sink
Why some leaks only appear when the tap is running
Simple checks you can do before calling a plumber
When to call a plumber, and how to find the best one for the job
Finding drips and pools of water under your kitchen sink can be a headache. But don't put off fixing the issue.
Left alone, even a small drip can warp cabinet floors, encourage mould, and turn into a bigger repair bill.
Here's how to work out why your kitchen sink is leaking underneath - and when to call in a plumber.
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How to find where a leak is coming from under a sink
Sometimes finding an under the kitchen sink leak can be straightforward. The leak might be obvious and the problem simply a matter of replacing a worn-out washer.
However, underneath the kitchen sink you'll find an entire network of water pipes generally squeezed into a confined area - which can make it tricky to pinpoint where it's coming from.
Try these steps to narrow it down:
Clear the cabinet. Empty everything out and wipe all the pipes and walls dry so you're starting from a clean, dry base.
Lay down kitchen paper. Place a couple of layers across the cabinet floor and check back regularly - leave it overnight if the leak is intermittent. A damp patch will point you upwards to the source.
Wrap pipes in tissue. Wrapping toilet paper around suspect pipework can help you pinpoint exactly which pipe or joint is weeping.
Run a sink test. Fill your sink - both if you have two - then let them drain while you watch closely. Run the dishwasher or waste disposal too, in case the leak is coming from an appliance rather than the sink itself.
Test the tap. Try every mode and spray setting if your tap has them. A fault here can look like it's coming from the pipework below.
You might need to replace your tap if it's old or faulty.
Remember that water can travel along a pipe before it drips, so the wettest spot isn't always directly below the actual leak. Trace pipework upwards from the puddle rather than assuming it's the closest joint.
Once you've tried all of these methods but still can't find the source of the leak, it's a good time to hire a local plumber.
They will have the expertise and specialist equipment to locate the leak and get the problem fixed efficiently first time round.
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6 common causes of a leak under the kitchen sink
Here are some of the most common causes for a kitchen sink leaking underneath.
1. Kitchen sink drain pipe leaking
Plastic plumbing pipes connected to the sink plug hole are one cause of leaks under the kitchen sink.
This includes connections and fittings connected to those pipes - both at the kitchen sink end and where they go into the waste system.
2. U-bend under sink leaking
U-bends (also known as waste traps) can also be a source of a kitchen sink plumbing leak.
They can become blocked and suffer from wear and tear. Also, the rubber washers at either end of a kitchen sink U-bend might become loose or dislodged and leak water.
3. Hot water supply leak
The hot water pipe under a kitchen sink is usually located on the left side of the sink. A leaking copper pipe under the sink can be connected to a dedicated, separate hot tap or a kitchen mixer tap.
Sometimes, these pipes and connections can leak due to movement, expansion and contraction, or just general wear and tear.
4. Cold water pipe leaking
The pipework that connects the mains water cold feed can also cause a leak under sinks.
Cold water pipes experience higher pressure than hot water pipes, so in this case, you might come across a sudden leak with lots of water.
Don't forget to check the stop taps for any leakage or break, too.
5. Kitchen sink overflow pipe leaking
The overflow on a kitchen sink is a small opening that stops the sink from overspilling and flooding if someone accidentally leaves the tap running when the plug is in.
It’s connected around the back of the sink to an overflow pipe that leads down into the drain.
A leaking overflow pipe can be commonly missed, but it's worth investigating.
6. Leaks from other appliances
Remember that there are often other appliances fitted near the sink.
So it might be that it's your washing machine or dishwasher that's leaking and not the sink plumbing connections.
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Leak only happens when the water is turned on?
A leak under the kitchen sink that only happens when the water is turned on usually points to a problem with your sink's plumbing.
Common causes can include:
Loose connections with pipes, connectors and joints
Damaged seals around sink or tap
Cracked pipes
Faulty water supply pipes
Drain leaks due to a faulty sink strainer or cracked drain pipe
Leak happens even when the water is off?
Working out the exact cause of a leak when the water is off requires prompt action - and the skills of a plumber. Otherwise, potential water damage and mould growth can arise if left unchecked.
Here are a few reasons why this might be happening:
Failing seals or gaskets due to wear and tear. Commonly seen around sink flanges, tap base or pipework connections
Pipe corrosion particularly older metal pipes
Damaged valves
Loose, worn or damaged water supply lines
Drainage issue such as a blockage
UK mains water pressure should typically sit between 1 and 4 bar. If your pressure is consistently higher, it's worth having a plumber check whether a pressure-reducing valve is needed - persistent high pressure is a common reason seals and washers fail early.
When to call a plumber vs. fix it yourself
Some fixes are genuinely DIY-friendly. Tightening a slip nut, swapping a worn washer, or reseating a drain basket with fresh plumber's putty are all reasonable weekend jobs if you're comfortable with basic tools.
Cracked pipes, failing valves, or a leak you can't locate after trying the steps above are better left to a hired plumber, since a wrong repair can make things worse or mask a bigger problem.
Find a plumber with Checkatrade
Get started finding a plumber for your kitchen sink leak by typing your postcode into our search tool. We'll show you the Checkatrade plumbers who operate in your area, so you can compare your options and get a quote.
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You can also post your job to get quotes from local plumbers, or download the Checkatrade app to keep all your conversations with tradespeople in one place.
FAQs
Turn off the water supply under the sink immediately, then work through the checks above to trace the source. Our guide on how to turn off the water under a sink walks through this step by step.
For a minor leak, wrapping the pipe in silicone tape or applying epoxy putty can hold things for a short while.
For a lasting fix, tighten slip nuts, replace worn rubber gaskets, or call a plumber to replace the damaged section properly.
Plumbers in the UK charge an average of £50 per hour, and fixing a leak usually only takes 1-2 hours. See our guide to plumber costs for more details.
U-bends wear over time, and the rubber washers at each end can loosen or deteriorate. Since the U-bend holds the water seal that stops sewer gases entering your home, a leaking one should be replaced promptly rather than left.
Yes. Constant high pressure puts extra strain on seals, washers, and pipe joints, making leaks more likely over time - even in pipework that isn't otherwise faulty.
It's rarely a true emergency, unless water is actively flooding your home. But left unchecked, moisture under a sink can warp cabinets, encourage mould, and eventually damage flooring - so even a drip is worth sorting within a few days at most.
Not usually. Most leaks from under sinks come from pipework or seals rather than the sink itself. If leaks keep recurring after repairs, or the sink shows visible cracks or corrosion, a replacement may be the more cost-effective option long term.
Not sure whether you need a plumber or someone with more specialist drainage expertise? Our guides can help you work out who to call and what to expect to pay.
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