Dripping Taps and Running Toilets: Causes and Fixes

Why traditional taps drip: washers

Older-style taps, particularly those with separate hot and cold handles, generally work by compressing a rubber or fibre washer against a valve seat to stop the flow of water. Every time the tap is turned on and off, that washer compresses slightly, and over months and years it hardens, flattens or perishes, meaning it no longer forms a complete seal, which is what produces the familiar drip from the spout.

Replacing the washer is usually a straightforward job: turn off the isolation valve or stopcock, remove the tap handle and headgear, swap the old washer for a new one of the correct size, and reassemble. It is one of the most cost-effective plumbing repairs there is, though getting the right size and type of washer matters, since an ill-fitting replacement will simply fail again quickly.

Why modern mixer taps drip: ceramic cartridges

Most contemporary mixer taps do not use a traditional washer at all, relying instead on a ceramic disc cartridge, a sealed unit with two precisely machined ceramic discs that rotate against each other to control flow and temperature. These are generally very durable, but they can still fail, either through a build-up of limescale and debris interfering with the discs, or simply through wear over many years of use.

Unlike a washer, a ceramic cartridge is not usually repairable and needs to be replaced as a whole unit, which means identifying the correct cartridge for the specific tap model, since they vary between manufacturers and are not always interchangeable.

Worn valve seats

If a tap keeps dripping even after a new washer has been fitted, the valve seat, the surface the washer presses against, may itself have become pitted or damaged, often from mineral deposits or years of a worn washer grinding against it. In this case, the seat can sometimes be reground using a seat-reseating tool to create a smooth surface again, or the tap may need replacing if the damage is significant or the tap body is old and difficult to source parts for.

Why toilets keep running: the fill valve

A toilet that continues to trickle or hiss long after flushing is usually down to the fill valve, sometimes called a ballcock, which controls how much water enters the cistern after each flush. If the valve fails to shut off fully, water will continue trickling into the cistern and eventually overflow into the overflow pipe, or simply run continuously if the level does not quite reach that point. This is often caused by a worn washer or diaphragm inside the valve, or occasionally a float that has become waterlogged and no longer rises correctly to shut the valve off.

Replacing a fill valve is a fairly routine repair: the water supply to the cistern is isolated, the old valve removed, and a new one fitted and adjusted so the water level sits just below the overflow, at the level marked inside most modern cisterns.

Why toilets keep running: the flush valve and flapper

The other common cause is the flush valve, the mechanism at the bottom of the cistern that releases water into the pan when you flush, often sealed by a rubber flapper or diaphragm washer. If this does not seal properly once the flush has finished, water continuously leaks from the cistern into the pan, which can sound like a faint trickle or hiss and often shows up as movement on the water surface in the pan even when nobody has flushed recently. Over time these rubber seals perish, warp slightly, or get caught by grit and limescale, all of which prevent a clean seal.

A simple way to check for this specific fault is to add a small amount of food colouring to the cistern water and wait without flushing; if colour appears in the pan within ten to fifteen minutes, the flush valve seal is letting water through and needs attention.

How much water this actually wastes

It is difficult to give an exact figure since it depends heavily on the size of the leak, but as an approximate guide, a slowly dripping tap can waste in the region of a few litres a day, while a toilet with a poor flush valve seal can waste considerably more, sometimes running into hundreds of litres over a month if the leak is more than a very faint trickle. Beyond the water bill itself, if it is a hot tap dripping, there is also the ongoing cost of heating water that simply goes down the drain.

Repair or replace

For most dripping taps, replacing a washer or cartridge is the sensible first step and is usually inexpensive, typically somewhere in the region of £70 to £150 including a call-out for a straightforward single tap repair, depending on the tap type and parts needed. If a tap is very old, the finish is worn, or parts are no longer available, replacing the whole tap can end up being better value than repeated repairs.

For toilets, replacing a fill valve or flush valve mechanism is usually a modest, worthwhile repair rather than something requiring a whole new toilet, unless the cistern or pan itself is cracked or the fittings are an unusual or obsolete size, in which case a full replacement may be the more practical long-term option.

Frequently asked questions

Is a dripping tap really worth fixing, or can I just live with it?

It is worth fixing fairly promptly, since a constant drip wastes water continuously, can stain the basin or bath beneath it over time, and a hot tap drip means paying to heat water that is never actually used.

How do I know if my toilet is silently running?

Listen for a faint hiss or trickle when nobody has flushed recently, check for movement on the water surface in the pan, or try the food colouring test in the cistern, which will show colour appearing in the pan if the flush valve is leaking.

Can I fix a dripping tap without turning off the water?

No, you should always isolate the water supply first, either at a nearby isolation valve or the main stopcock, before removing a tap handle or headgear, otherwise you risk an uncontrolled flow of water into the room.

Why does my tap drip more after the plumber has just fixed it?

This can happen if the wrong size washer or cartridge was fitted, or if the valve seat is damaged and needs attention as well, so it is worth going back to whoever carried out the repair if the drip returns quickly.

Are ceramic disc taps more reliable than traditional washer taps?

Generally yes, ceramic cartridges tend to last longer than rubber washers, though they are not immune to failure, particularly in hard water areas where limescale can interfere with the discs over time.