Leak under the sink: fix it yourself or call a plumber?

Find the first wet point before tightening anything.

The answer in 2 lines. Stop using the sink and any connected appliance. If water is escaping from a supply pipe, isolate it at a working local valve or the internal stop tap. Keep away from wet electrical equipment. Once the area is safe, dry the cupboard and look for the highest wet point. A straightforward plastic waste connection may allow a simple adjustment, but leaking supply hoses, damaged valves and concealed pipework need a qualified plumber. If you rent, report the leak and obtain permission before repairing it yourself.

The first steps

Stop using the sink, dishwasher and washing machine if they discharge through the affected pipework.
If the leak is from a pressurised pipe or its origin is uncertain, close a clearly identified local isolating valve or the internal stop tap. Do not force a stuck valve.
If there is no electrical danger, move cupboard contents, catch drips and dry accessible pipework. Photograph the first point that becomes wet.

Stop: danger

Water near a socket, dishwasher connection or waste disposal unit: keep away from wet equipment. Switch off electricity only at a safely accessible dry consumer unit. Use Electrical Safety First's guidance to arrange checks before reusing equipment affected by water.
If drain cleaner has been used, do not undo the trap or put your hands into the waste water. Tell the plumber what product was used.
An uncontrolled leak or a bulging ceiling below needs urgent attention. Keep people away from the affected area and contact the responsible repair service.

Work out whether it is supply or waste water

A tap being closed does not remove pressure from its supply connectors. Water appearing while nothing is being used may come from a supply connection, although a slow drip travelling along another surface can be misleading. Keep the supply isolated if that is suspected.

A leak appearing only as the sink empties points towards the sink outlet, trap or waste pipe. Water can also enter around the tap base or sink edge and run down into the cupboard. Check from above as well as below. A wet cupboard floor shows where water collects, not necessarily where it starts.

A limited check you can make safely

Only investigate if everything is accessible, there is no chemical or electrical hazard, and you are confident the supply is controlled. Dry visible joints and use kitchen paper to identify fresh moisture. Do not reopen an uncontrolled supply leak merely to reproduce it.

If you suspect the waste assembly, a small amount of clean water poured into the sink can help reveal a drip without reopening the supply. Stop immediately if water escapes into the cupboard or floor. Never run a connected appliance just to reproduce a leak: it may release much more water than you can contain.

What not to do

Forcing plastic waste nuts with pliers: you can crack the fitting or distort a seal.
Trying to cure every leak by tightening harder; the washer may be displaced or the component damaged.
Using adhesive or sealant as a substitute for replacing a failed pressurised connector.
Leaving a bowl beneath the leak as a permanent repair or using the cupboard before checking that it stays dry.

Where a small DIY job ends

On a straightforward accessible plastic trap, a visibly loose hand-tightened connection may be worth gently reseating in accordance with its instructions. Do this only if you own the installation or have permission. If it still leaks, stop: a damaged or incorrectly seated washer needs the correct replacement, and dismantling unfamiliar pipework can create another leak.

Call a qualified plumber for a leaking flexible supply hose, corroded connector, cracked fitting, faulty isolating valve, soldered joint or pipe disappearing into a wall or floor. The same applies if isolation does not stop the water, the leak returns after an adjustment, or damage extends beyond the cupboard. Do not work on electrical connections or sealed heating equipment.

Arrange the repair and record the damage

Tell the plumber whether the leak occurs continuously, during draining or during appliance use. Send clear photographs and explain which valve has been closed. Follow the leak isolation guidance for locating the stop tap and avoiding force on a stuck valve.

Keep photographs, repair messages and receipts. If there is insured damage, check your policy and contact your insurer about approval and reporting requirements; there is no single reporting period for every policy. Tell your managing agent if communal pipework or another flat may be affected.

Good to know

In England, landlords generally repair sinks and associated pipes and drains; tenants can be responsible for damage they cause. Read GOV.UK's repairs guidance, report the fault promptly and check permission before doing work yourself. Tenancy rules differ elsewhere in the UK.
After a repair, check the cupboard while the sink drains and again after normal use. Keep the area clear enough to spot returning moisture, and arrange further investigation if it remains damp or smells musty.

Illustrative example: in Bristol, Priya finds water beneath her sink. She stops using it and tells her landlord. With the cupboard dry and electrics unaffected, she notices a drip from the waste connection when a little clean water drains through. She sends photographs; the landlord arranges a repair rather than asking her to replace the tap's supply hoses.

A made-up story, for illustration.

Bobby

Sources, verification, confidence

Verified on 4 November 2026, for England. Confidence: high for isolation advice, electrical precautions and general renting responsibilities; medium for identifying the source and deciding whether an individual waste fitting permits a simple adjustment. The checks are practical triage, not a diagnosis or a replacement for installation instructions.