A tap usually keeps dripping after it is turned off because the part that seals the water in has worn, cracked or become coated in limescale. In older taps this is often the rubber washer, while in many modern taps it is the ceramic cartridge or one of its seals.
The drip will rarely fix itself. It may stay the same for a while, but it often gets slowly worse as the worn part breaks down further.
Washers in Traditional Taps
Taps with a rising handle that turns several times from off to on usually close by pressing a rubber washer onto a seat inside the tap. Each time the tap is turned off, the washer is squeezed. Over time it hardens, splits or wears unevenly.
The seat it presses against can also wear or pick up scale. If the seat is rough, even a new washer may not seal well, which is one reason a drip can return after a quick fix.
Ceramic Cartridges in Modern Taps
Quarter-turn taps and most lever mixers use two ceramic discs that slide over each other. When the holes line up, water flows. When they do not, it stops. Grit, scale or a chip on a disc can stop them sealing fully, leaving a steady drip.
Small rubber seals at the base of the cartridge can also wear. In a mixer, a drip that is warm may point to the hot side, while a cold drip may point to the cold side, though this is not always reliable.
Why It Is Worth Fixing
A dripping tap wastes water and, if you are on a water meter, that waste is added to your bill. Thames Water includes fixing dripping taps in its advice on looking after your plumbing.
Drips can also leave limescale marks or stains in the sink or basin, and a hot tap that drips wastes heated water too. In some cases, a small drip is the first sign of a part that may fail more suddenly later.
Do not try to stop a drip by turning the tap off harder. This puts extra strain on the washer or cartridge and can make the problem worse.
Safe Next Steps
Put a cloth in the sink to quieten the noise and catch the water if it is bothering you. If the drip becomes a steady run, you can close the isolation valve under the tap if it turns easily, or use the stopcock. Never force a stiff valve.
Note whether the tap has a rising handle or a quarter-turn lever, and whether the drip is hot or cold. Our leaking tap repair service in Oxford can use these details to bring the likely parts and sort the drip at its source.