Dripping Tap: The Causes, the Repair, and When a New Washer Will Not Help

What a dripping tap is actually costing

A drip is the least urgent plumbing fault there is and one of the most persistent, which is why it stays unrepaired for years. The case for dealing with it is made on three separate grounds, and only one of them is about noise.

The first is volume. WaterSafe, the national accreditation body for approved plumbers, puts a leaking tap at up to 5,500 litres of water a year. On a metered supply that is a charge for water nobody used. On an unmetered supply it costs nothing directly, which is precisely why unmetered households leave drips running longest.

The second is the damage the drip does on its way. London is a hard water area, and water evaporating continuously in one spot deposits everything it was carrying. That produces the limescale ring that etches enamel, the green stain on a copper or brass waste, and the corroded crust that eventually seizes a waste fitting into its tail. Our article on hard water and limescale in London homes covers why the deposits form as fast as they do here.

The third is regulatory. The Water Supply (Water Fittings) Regulations 1999 require that water fittings are of an appropriate quality and standard and that they do not cause waste, misuse, undue consumption or contamination of water supplied by a water undertaker. A fitting left dripping is a fitting causing waste, and that obligation applies to the person using the supply rather than only to the plumber who installed it.

There is a fourth reason that applies to landlords and managing agents specifically. A drip is a visible, trivially verifiable item of disrepair, and a property handed over with one signals how the rest of the maintenance has been handled. In a dispute over a larger and less visible failure later, the small things that were left are the ones quoted back.

Identify the tap before you touch it

Almost every failed repair starts here. Taps that look similar work on entirely different principles, and buying a washer for a tap that has no washer in it is the single most common wasted trip to a merchant.

Type	How you recognise it	What actually wears
Rising spindle, washer type	Handle turns several full rotations; head rises as it opens	Rubber washer, and the brass seat it closes against
Quarter turn, ceramic disc	Handle moves about 90 degrees from off to full	Ceramic disc cartridge, and its O-rings
Monobloc mixer, single lever	One lever controls flow and temperature together	Single ceramic cartridge, and the spout O-rings
Monobloc mixer, two handle	Two small handles on one body, one spout	Two cartridges or two washer valves, depending on age
Bib tap or outside tap	Wall mounted, threaded outlet, often a hose union	Washer, seat, and frequently the gland

The quickest way to tell

Turn the handle from fully off to fully on and count. A quarter or half turn means ceramic discs and a cartridge. Two or three full turns means a rising spindle and a washer. If the handle is a single lever, it is a cartridge regardless of what the body looks like. Taps fitted to British homes before the 1990s are overwhelmingly washer type; most installed since are ceramic, though traditional styling is still sold with both mechanisms inside, so the count matters more than the appearance.

Where the drip is coming from, and what it means

A tap can leak from four places, and they are four different faults with four different repairs. Work out which before you strip anything.

Where water appears	What it indicates	Repair
From the spout, tap fully closed	Washer or cartridge is not sealing	Replace the washer or cartridge; check the seat
Around the handle when the tap is open	Gland packing or O-ring on the spindle has failed	Repack the gland or replace the spindle O-rings
From the base of the tap onto the worktop	Body seal or the sealing washer under the tap	Lift the tap and replace the base seal
Under the sink, at the tails	Flexible connector, compression joint or service valve	Remake the joint or replace the connector
From the swivel of a mixer spout	Spout O-rings perished	Replace the O-ring set on the spout

The distinction that matters most is between the first row and the last. A drip from the spout is a tap fault and it wastes water at a rate you can see. A leak at the tails under the sink wets a cupboard base and a floor, does it silently, and is the one that turns into a claim. If the cupboard under your sink is damp and the tap drips, treat those as two separate investigations.

The repair sequence

What to have ready before you start

A tap repair goes wrong through missing parts far more often than through missing skill. Gather these first, because the shops shut and the water stays off.

• An adjustable spanner and, ideally, a basin wrench for nuts you cannot reach from above
• A flat screwdriver for the service valves and a small cross head for the handle screw
• A set of tap washers in the common sizes, or the exact cartridge if the tap is ceramic
• PTFE tape, a replacement fibre or nylon sealing washer, and silicone grease for O-rings
• An old towel for the basin, a container for the water still in the pipe, and a torch
• Penetrating oil, applied an hour beforehand to anything that looks corroded

Isolating properly

Most kitchen and basin taps installed in the last thirty years have a service valve on each tail under the unit, operated with a flat screwdriver: a quarter turn so the slot sits across the pipe closes it. Where there is no service valve, close the internal stopcock, and if the tap is fed from a loft tank rather than the mains, close the gate valve on the tank outlet instead. Our guide to turning off the water in a London property covers the order and the traps.

Two things to do before dismantling: open the tap and leave it open to drain and to prove the isolation has worked, and put the plug in the basin, because the small brass screw that falls down a waste is the reason a fifteen minute job becomes an afternoon.

• Isolate at the service valve, stopcock or tank valve, then open the tap to confirm
• Plug the waste and lay a towel in the basin to protect the finish
• Prise off the handle cap, remove the retaining screw and lift the handle
• Unscrew the headgear with a spanner, holding the tap body so it does not turn on its tails
• Replace the washer, or lift out and replace the cartridge with an identical part
• Inspect the brass seat for pitting or scale before reassembling
• Reassemble, open the isolation slowly, and check for weeping at the gland as well as at the spout

Holding the tap body while turning the headgear is the step most often skipped, and the consequence is that the tap twists on its tails and starts a leak under the sink that was not there before. On an old tap with corroded tails, that twist can crack a joint that had been sound for decades.

When a new washer will not fix it

A replacement washer solves the problem only when the washer is the problem, and on an old tap it frequently is not. Four cases account for most of the repairs that drip again within a week.

The first is a damaged seat. The washer closes against a brass seating inside the tap body, and years of grit, scale and over-tightening pit that surface. A new washer pressed against a pitted seat will not seal. The remedy is reseating, either by cutting the seat true with a reseating tool or by fitting a nylon seat and washer set that takes up the imperfection. Diagnosing this is easy: if the drip persists after a new washer, the seat is the reason.

Reseating, and its limits

Reseating cuts a fresh flat face on the brass seat so a new washer has something true to close against, and on a tap worth keeping it is a sound repair. It is not unlimited. Every cut removes metal from a seat that was only a few millimetres deep to begin with, so a tap that has been reseated once has less material left and a tap that has been reseated twice is usually finished. A nylon seat and washer set, which drops a replacement seating face into the existing body, avoids cutting at all and is often the better answer on an older tap. Where the body itself is corroded rather than just the seat, neither approach will hold, and the tap has reached the end of its life.

The second is a cartridge that cannot be matched. Ceramic cartridges are not standardised, so replacing one means identifying the manufacturer and model, and on a tap from a discontinued range the part may no longer exist. Measuring the cartridge and taking the old one to a merchant is far more reliable than describing it.

The third is corroded tails and unions. On a tap that has been in place for decades, the copper tails and their nuts may be so far gone that any attempt to work on the tap disturbs them. In that situation the sensible sequence is to plan for replacement rather than repair, with the isolation and materials for it on hand before anything is loosened.

The fourth is not the tap at all. A tap that is dripping while somebody is running water elsewhere in the house, or one that drips only at night, is often responding to pressure rather than to a worn seal, and high static pressure is a fault in its own right. The same goes for the reverse case, in which the real problem is a tap that has never sealed properly because a pressure reducing valve was never fitted where the incoming pressure justified one.

The hot tap that drips after the cylinder heats

A specific case is worth separating out because it is not a tap fault and repairing the tap will not cure it. Water expands as it is heated, and a hot water cylinder heating a full charge of water has to put that expansion somewhere. On an open vented system it returns up the vent pipe to the feed and expansion cistern. On an unvented system it is absorbed by an expansion vessel or an internal air bubble.

When that accommodation fails on an unvented system, the pressure rise has to go somewhere, and a hot tap that drips for a period after the cylinder has heated and then stops is one of the ways it shows. So is a tundish that discharges after a heating cycle. Neither is fixed by a washer.

This is also a point where competence is defined in law rather than by preference. An unvented hot water storage system is subject to the requirements of Approved Document G of the Building Regulations, and its installation and maintenance is work for a competent person holding the relevant qualification. Its safety devices, including the expansion vessel, the expansion relief valve and the temperature and pressure relief valve, are not householder maintenance. If a tundish is discharging, that is a diagnosis to book rather than a drip to live with.

Repair or replace, and the rules that apply

On a tap under about ten years old with an available cartridge, repair is straightforward and cheap. On a tap of unknown age with corroded tails, a pitted seat and a discontinued cartridge, the labour to repair it approaches the labour to replace it, and the replacement resets the clock.

Situation	Lean towards	Why
Modern tap, cartridge available	Repair	Part is cheap and the job is short
Traditional washer tap, sound seat	Repair	Washers are standard and reseating is possible
Pitted seat that has already been reseated once	Replace	There is a limit to how much metal can be cut away
Corroded tails or seized back nut	Replace	The disturbance needed to repair is the same as to replace
Discontinued cartridge, no match	Replace	Part availability decides it
Single lever mixer on a low pressure supply	Replace with a suitable model	The wrong tap for the supply will keep failing

Two regulatory points apply to a replacement. Fittings must comply with the Water Supply (Water Fittings) Regulations 1999, and a WRAS approval or an equivalent recognised certification is the usual way of demonstrating that a fitting is of an appropriate quality and standard. And the Regulations also govern backflow prevention, which is why a tap serving an outside supply or a hose connection has requirements a kitchen tap does not; our article on outside taps and why they leak covers that case and the frost exposure that goes with it.

Finally, apply the same thinking to the rest of the property while you are at it. A running toilet wastes far more than a dripping tap and makes no noise at all, and the cistern is a more common source of a high metered bill than any tap. Our guides to fixing a leaking toilet cistern and to a running toilet and what the repair costs cover the checks that take five minutes each.