Most leaks under a sink come from the waste trap and its washers, a weeping compression fitting, a perished tap hose, or a dishwasher or washing machine connection. If it drips all the time, it is usually on the supply side. If it only leaks when the tap runs or the sink drains, it is usually the waste or a seal. First put a bowl underneath, turn off the isolation valve or stopcock, and keep water away from sockets.
What should I do right now?
Catch the water, stop the supply and keep it away from electrics. A drip is rarely an emergency, but a split hose can flood a kitchen quickly.
- Put a bowl or tray underneath
- Then clear the cupboard so you can see.
- Turn off the isolation valves
- Small valves on the tap pipes. A quarter turn so the slot sits across the pipe.
- Or use the stopcock
- Often under the kitchen sink. Turn it clockwise, and do not force it.
- Keep water off electrics
- If an appliance socket or spur is wet, switch off at the fuse box.
- Stop using the sink and appliances
- No dishwasher or washing machine cycles until it is found.
Is it the supply pipe or the waste pipe?
Watch when it leaks. That clue narrows it down fastest.
- Drips all the time
- A supply pipe, valve, tap hose or fitting. These are under pressure even when nothing is on.
- Only when the tap runs
- The tap base, the tap hoses, or water running off the worktop edge.
- Only when the sink drains
- The waste trap, its washers, the plug fitting or a cracked waste.
- Only when an appliance runs
- Its hose, valve or the waste connection on the trap.
How do I find the exact spot with the kitchen-roll test?
Dry everything, then let the water show you where it comes from. Water runs along pipes before it drips, so the wet patch is often not where the leak is.
Wipe every pipe, joint and the underside of the sink dry. Wrap kitchen roll around each joint, or lay sheets underneath. Then test one thing at a time: tap off for ten minutes, hot tap, cold tap, fill the sink and pull the plug, then an appliance cycle. The first sheet to get wet marks the leak.
What are the common causes, and how do I tell?
These are the usual culprits, roughly most likely first:
- Waste trap and washers
- Loose plastic nuts or a worn or missing washer. Drips when draining.
- Compression fittings
- A brass nut and olive on copper pipe. A slow weep, often with green staining.
- Flexible tap tails
- Braided hoses on mixer taps can perish, corrode or split, often at the crimp.
- Appliance connections
- A loose hose on a valve, or a hose clip on the trap spigot.
- Isolation valves
- Can weep at the slotted spindle, especially if turned after years untouched.
- Sink seal or tap base
- Water gets under the sink rim or through the tap hole, then down the cupboard.
- A cracked waste
- Plastic waste fittings or the plug fitting can crack with age or a knock.
What can I safely check or fix myself?
Plenty, as long as nothing electrical is wet. Hand-tighten the plastic nuts on the waste trap; if one still drips, undo it, check the washer sits flat and refit it.
A compression fitting that weeps may stop with a gentle quarter turn. Do not overtighten, as that crushes the olive and makes it worse. Check braided tap hoses for rust spots, bulges or frayed strands, and look at appliance hoses for cracks. Storing bleach or strong cleaners under the sink can corrode braided hoses, so move them.
If a supply fitting keeps weeping, a hose looks damaged, or the leak is above the sink, it is time to call someone.
What will a plumber do to fix it?
They dry the area, run each part in turn and watch, much like the kitchen-roll test, then repair the faulty part and test it under pressure.
Typical repairs are a new trap or washers, a new olive or fitting, replacement tap hoses, a new isolation valve or appliance hose, or resealing the sink and tap. If tap tails are damaged, changing the tap can be simpler. Most are done in one short visit.
Is my sink cupboard damaged, and does it need replacing?
Check the cupboard base once the leak is fixed. Most kitchen units are made of chipboard, which swells and crumbles when it stays wet, and can grow mould underneath.
If the base is only stained, dry it out with the doors open and a fan if you have one. If it is soft, swollen or sagging, it usually needs replacing, and the flooring or kickboard below may need checking too. That work is separate from the leak repair, and any quote should say clearly whether it is included.
How do I stop it happening again?
A quick look under the sink now and then catches most leaks early.
- Check every few months
- Look and feel for damp joints with a torch.
- Keep chemicals elsewhere
- Bleach fumes can attack braided hoses.
- Don't overload the cupboard
- Knocking pipes and traps loosens joints.
- Reseal the sink rim
- Replace tired silicone before water gets under it.
- Know your valves
- Make sure you can find and turn the stopcock and isolation valves.
Questions
Is a slow drip under the sink urgent?
Not usually an emergency, but do not leave it. A slow drip can soak the cupboard base, rot flooring and grow mould behind units without you noticing. Keep a container under it, check it daily and get it fixed soon.
Why does my sink only leak when the dishwasher runs?
The dishwasher pumps its waste water into a spigot on the sink trap or waste. A loose hose clip, a split hose or a partly blocked trap can make it leak only during a cycle. Check the clip and hose first.
How long do braided tap hoses last?
There is no fixed lifespan. They can last many years, but they can fail sooner with corrosion, kinking or chemicals stored nearby. Rust spots, bulges or broken strands mean replace them. Some makers suggest checking them regularly, so follow their advice.
Can I use sealant tape or putty to stop the leak?
It can hold briefly in an emergency, but it is not a repair. Supply leaks are under mains pressure and will break through. Waste leaks usually need a washer or new trap. Turn the water off and fix the part properly.
Will my insurance cover water damage from a sink leak?
Many policies cover damage caused by an escape of water, but often not the repair of the leaking part itself, and some exclude gradual leaks. Check your policy, take photos before cleaning up and keep the repair invoice.
What photos help you price a sink leak?
A wide shot of the open cupboard, close-ups of the wet joints, the tap above and any damage to the base. Send them with any other jobs and we reply within 24 hours with one fixed price, agreed before work starts.