Quick answer
Stop using the sink and identify whether the leak occurs from the tap supply, waste pipe or an appliance connection. Close the relevant isolation valve if safe; if water continues or the source is uncertain, turn off the stopcock and arrange a repair.
Protect the cupboard and stay safe
A small leak under a sink can soak the cabinet base and spread into flooring before it is obvious. Remove stored items carefully and dry the area enough to see where new water appears. Do not reach into a wet cupboard if there are electrical sockets, a waste disposal unit or appliance connections in the water.
If water is near electrical equipment, do not touch it. Isolate the electricity only at a dry, safely accessible consumer unit. Stop using the dishwasher or washing machine if its hose or connection may be involved.
Locate and isolate the likely source
- 1Dry visible pipes and connections, then briefly run cold water only if it is safe, watching for a fresh drip. Check separately around the tap tails, isolation valves, waste trap and appliance hoses.
- 2A leak that appears only while the tap drains may point to the waste side; a leak that continues when fixtures are unused may involve a pressurised supply. These are clues, not a definite diagnosis.
- 3Close the small isolation valve on the affected supply if you can identify it and it turns freely. If the leak persists or you are unsure which valve controls it, close the main stopcock if safe.
- 4Place a container or towel beneath a drip and avoid overtightening plastic fittings. A damaged joint can worsen if forced.
Arrange a suitable repair
A plumber can inspect the connection and replace a failed washer, valve, trap or hose as appropriate. Do not rely on tape around a pressurised joint as a permanent repair. Once the leak is stopped, dry the cupboard and check for swelling, mould or damage to nearby flooring.
TraceFix Plumbing offers emergency plumbing in Birmingham and London. Take photographs before moving items if you may need to discuss the damage with your insurer. Check your policy for requirements before authorising non-urgent reinstatement work.
When to call a plumber
- The leak continues after closing a local isolation valve.
- You cannot identify the correct valve or the stopcock is stuck.
- Water has reached sockets, appliances, flooring or the room below.
- The pipework is corroded, concealed or damaged by a failed fitting.