Water leaking under the kitchen sink: how to find and fix it

Before you touch anything: dry everything out and get ready

Clear the cabinet completely and wipe every surface dry with a cloth or kitchen roll, including the underside of the sink bowl, the pipework, and the cabinet floor and walls. A wet mess makes it impossible to see where new water is coming from, so start from bone dry.

Have a torch, an adjustable spanner, a bucket, some old towels, and plumber's tape (PTFE tape) to hand. Slide a sheet of dry paper or cardboard under the whole assembly — it shows you exactly where the first drop lands.

Turn off the water at the isolation valves under the sink if you have them, or at the stopcock for the flat if you don't. This stops the problem getting worse while you work out what's causing it.

Finding the leak: the dry-and-test method

With everything dry, turn the water back on and run the tap for a minute, then look and feel along every joint — trap, hoses, dishwasher connection, tap base — before checking the paper underneath for the first wet spot.

Run the tap on cold, then hot, then let the sink drain fully and watch the trap for a few seconds after. A leak that appears only during draining points to the trap or waste pipe; one that appears the moment the tap runs points to the supply side or the tap base itself.

If you have a dishwasher connected, run a short cycle on its own with the sink untouched. That isolates whether the water is coming from the dishwasher's own connection rather than anything you've just been testing.

The trap and waste connections — usually a DIY job

The trap is the U- or S-shaped pipe under the plughole, and it's the most common source of a slow drip. Over time the two plastic nuts that hold it together can loosen from vibration, or the rubber washer inside can perish and stop sealing properly.

Undo the nuts by hand or with gentle help from a wrench, check the washer is seated square and isn't cracked or flattened, and do the nut back up hand-tight plus a small turn with the wrench — not fully tight with force, which can crack the plastic thread.

If the washer is damaged, a replacement costs very little at any hardware shop and takes minutes to fit. This is one of the few plumbing jobs that's genuinely easier to do yourself than to book someone for a 45 € call-out.

• Wipe the trap and both nuts dry
• Run water and watch for drips at each joint
• Hand-tighten nuts, then a small turn with a wrench
• Replace a cracked or flattened washer
• Re-test with the cabinet floor lined with dry paper

Supply hoses and the dishwasher connection

The flexible supply hoses running from the isolation valves to the tap can weep at either end — where they screw onto the valve, or where they screw into the underside of the tap. A slow leak here is often just the compression nut having worked loose.

Tighten with an adjustable spanner a quarter turn at a time, testing after each turn. If tightening doesn't stop it, the rubber seal inside the fitting has likely perished, and the hose is a straightforward like-for-like replacement rather than a repair.

The dishwasher's inlet hose connects the same way, usually to its own isolation valve or a T-piece off the sink's cold supply. Check that connection is fully seated and the nut is snug — dishwasher connections work loose over years of the appliance being pulled out and pushed back for cleaning.

The tap base — sometimes simple, sometimes not

If the water is tracking down from where the tap body meets the sink or worktop, the seal at the base has likely failed. On many taps this is an O-ring or a rubber gasket that can be replaced without removing the whole tap, provided you can get underneath it comfortably.

If the tap has to come off to reach the seal, or if the base is corroded, cracked, or the tap itself is old enough that it's due for replacement anyway, that's the point to stop rather than force it. A tap forced back on with a damaged thread often leaks worse than before.

We offer tap replacement from 55 € per job, which includes fitting a like-for-like or a tap you've bought yourself, and it's often the more sensible option once a tap is past ten or fifteen years old rather than chasing a seal that will fail again soon.

When to stop and call someone instead of carrying on

Call a plumber if you've tightened every joint and dried everything and the leak still returns, if the water is discoloured or smells, if a fitting is corroded solid and won't budge without risking damage, or if you're not confident shutting off and restoring the water supply.

Persistent under-sink damp left unaddressed can swell the cabinet base and, in a shared building, travel down to the flat below — worth fixing properly rather than mopping up weekly.

Our plumbing work starts from 45 € per hour, with a 25 € call-out in Tallinn that's deducted from the bill if the work goes ahead, and any job we do carries 24 months' guarantee on the work itself.