Is a Small Leak Under the Kitchen Sink Actually an Emergency?

Nearly everyone finds it the same way: you reach under the sink for the washing-up liquid and the cupboard floor is damp, or there's a faint musty smell that wasn't there last month. It's not spraying, it's not flooding — so is it actually urgent?

The honest answer is that a small under-sink leak is rarely an emergency in the next hour, but it is almost always more expensive the longer it's left. Water in a chipboard cabinet base does its damage quietly.

This is the one distinction that decides how urgent it is.

Dry everything out completely with a towel. Then, without running any water, wait 20 minutes and look again.

• Wet again with no taps used: the leak is on a pressurised supply pipe or a flexi hose. That water is under mains pressure, it will only get worse, and a failed flexi hose can empty gallons into a kitchen in minutes. Treat it as urgent.
• Only wet after you fill the sink or run the washing machine: it's on the waste side — a trap, a waste connection or the appliance hose. Less dramatic, but it will rot the cabinet and can bring damp and mould.

The waste trap. Plastic bottle traps and P-traps rely on a rubber washer compressed by a hand-tightened nut. They loosen, the washer hardens, and the trap weeps at the joint. Most common cause by a distance.

Flexible tap connectors. The braided hoses feeding the mixer tap have a rubber liner and a limited life. When they fail they can fail suddenly. Any hose showing rust spots or bulging on the braid should be replaced now, not later.

Isolation valves. The small screwdriver-slot valves on the supply pipes weep at the spindle over time — often a slow bead that runs down the pipe and drips off the lowest point, which is why the wet patch is rarely directly under the fault.

The appliance connection. Washing machines and dishwashers tee off under the sink. A loose jubilee clip on the drain hose or a perished self-cutting valve leaks only during a cycle.

The sink seal itself. If the silicone round the sink rim or the sealing washer under the waste has failed, water tracks down the underside of the bowl and drips from the back of the cupboard.

Supply pipework. Less common, but copper compression joints and older push-fit connections do relax. If the damp is on the pipe run rather than at a fitting, it needs proper pipe repair.

Kitchen cabinet bases are usually moisture-resistant chipboard, not solid timber. Once the edge banding is breached, the board swells, delaminates and never recovers — you can't dry it back into shape. From there, water spreads along the plinth to neighbouring units and under vinyl or laminate flooring, where it lifts the joints.

Then there's what you can't see. A cupboard that stays damp is a closed, unventilated, room-temperature box — ideal conditions for mould, which is a genuine health concern in homes with asthma or young children. In flats and terraces, a persistent leak that reaches the floor structure becomes a neighbour's problem too, and insurers take a dim view of damage that has clearly been developing for months.

1. Look for isolation valves on the pipes under the sink. Turn the slot so it sits across the pipe — that's off. This stops the supply to the tap without affecting the rest of the house.
2. If there are no isolation valves, find your internal stopcock (commonly under the sink itself, or in a downstairs cloakroom or hallway cupboard) and turn it clockwise. Worth knowing where yours is before you need it.
3. Put a washing-up bowl under the drip and empty the cupboard completely so nothing else gets ruined.
4. Leave the cupboard doors open to ventilate, and get a fan or dehumidifier on it if you have one.
5. Don't over-tighten plastic nuts. Hand tight plus a nudge is the limit — cracking a trap turns a drip into a flood.

Call straight away, at any hour, if water is coming out under pressure and you can't isolate it, if the leak is reaching electrical sockets, an appliance or a consumer unit, if water is coming through a ceiling below, or if the stopcock is seized and won't shut off. Our emergency plumber service covers Kingston upon Thames and the surrounding area around the clock.

For everything else — the slow weep, the damp base, the drip that only happens on a wash cycle — book a normal appointment, but book it this week rather than next month.

Maxfix repairs under-sink leaks across Kingston, Surbiton, New Malden and Richmond, usually in a single visit. See our under-sink leak repair and kitchen plumbing pages, call 020 3488 0912, or request a free quote. We're the Kingston plumber homeowners call when they'd rather it was done once.