What the sound of running water with taps off usually means
The sound of running water with taps off usually comes from something filling up or from water escaping. Toilet cisterns, the cold water tank in the loft and some appliances refill on their own after use. Central heating moving round the radiators can sound similar. Once nothing should be filling, look at your water meter. If it is still moving, water is leaving your pipes somewhere.
The next clues are where the sound is loudest and whether it stops when you close the stop tap. A pipe that hisses quietly day and night can waste a great deal of water before any damp shows, especially under a solid floor or a lawn. Often the first sign is a letter from the water company or a bill that jumps.
Normal noises to rule out first
Plenty of ordinary things make a house sound as though a tap has been left on. Most of them stop once the job is done: a cistern refills, the loft tank tops up, a washing machine finishes its cycle. So give it time after the last flush, bath or load of washing before you decide anything. Heating can run for hours, so switch it off while you listen.
One item on the list below is a real leak, just not a hidden one: a cistern that never stops filling, sending water into the pan. You can often see a thin ripple running down the back of the bowl long after the flush. It moves the meter too, so fix it or rule it out first. Work through the list, switching off or waiting out what you can:
A toilet cistern refilling, or trickling into the pan without stopping
The cold water tank in the loft topping up
Central heating pumping water round the radiators
A softener, dishwasher or washing machine mid cycle
Rain running down a pipe boxed into a wall
The meter check
Find your water meter: usually outside under a cover in the footpath or front garden, sometimes indoors near the stop tap. With every tap, appliance and cistern quiet, look at the small wheel or flow indicator on its face. If it is not moving, no water is passing through the meter, and the sound is more likely heating, rain or next door. If it is moving, something is using water.
Now split the house from the ground outside. Shut the indoor stop tap, which in many homes sits below the kitchen sink, and check again. A meter that stops means the water was going somewhere inside. An outside meter that carries on turning means water is escaping underground, on your stretch of pipe between that meter and the house. A second person standing by the noise makes this quicker.
An indoor meter cannot see water lost on the buried pipe before it, so a leak there will not move it. With no meter at all, close the stop tap and listen: a sound that stops was water flowing into the house. If the meter is not moving but your boiler keeps losing pressure, look at the heating instead. On a sealed system, the kind most modern boilers use, a leak shows as falling pressure on the boiler gauge, not on the water meter.
Where the noise is loudest
Listen when the house is quiet, late in the evening or early in the morning. Move slowly from room to room and listen close to the floor by the kitchen sink, in the airing cupboard, under the stairs, at the loft hatch and on walls below bathrooms. An old trick helps: rest the tip of a long screwdriver on a pipe or the stop tap and hold the handle to your ear.
In terraces, semis and flats, sound travels through shared walls and floors, so a noise may be coming from next door or the flat above. If your meter does not budge while everything is off, mention the noise to your neighbour, who may want to run the same check. Where you hear it loudest can suggest a cause:
By the stop tap: see the next section
Over a warm patch of floor: possibly a hot pipe leaking beneath
On a wall below a bathroom: the pipes feeding that room
In the loft: the tank's float valve or loft pipework
At the outside meter: your water company can check it
What a hiss near the stop tap can mean
The stop tap is where the supply pipe comes up into the house, and older metal pipe in particular carries sound a long way. So a hiss you hear there may start somewhere else. Close the stop tap and listen. If the hiss stops, water was being drawn through it to something inside the house: a leak indoors, or a cistern, tank or appliance still filling.
If the hiss carries on with the stop tap shut and an outside meter keeps moving, the water is escaping on the pipe before the stop tap. That points to the buried length between the meter and the house, with the sound travelling along the pipe to you. If the outside meter has stopped but the hiss continues, the noise may be next door's pipes, your heating, or a leak on the water company's side of the meter, which is the company's to look at.
A stop tap that has not been turned for years can be stiff, and forcing it can break it or start a leak at the spindle. If it will not shut fully, this test is unreliable, and our testing on the day needs a stop tap that closes properly. Tell us about it when you ring.
How acoustic listening uses the sound
The noise you can hear is the same thing we follow, only far more closely. A ground microphone placed on the floor or the ground picks up the noise water makes as it escapes from a pipe under mains pressure. Moved step by step along the line of the pipe, it shows where the sound is strongest, which is usually close to the leak. Nothing is cut open while we search; any opening up starts at the spot we mark.
Plastic pipe, a pipe buried deep, soft soil and traffic noise all weaken the sound, and a leak that stops and starts may be quiet when we arrive. Where listening is not enough, we switch to tracer gas, a hydrogen and nitrogen mix, or to thermal imaging if the pipe carries hot water. Either way, a spot is only marked and photographed after a second, different test has pointed to the same place.
What to do next
Write down what you found: when you hear the sound, where it is loudest, whether it stops with the stop tap closed and what the meter did. Keep any letter from the water company. If water is showing through a ceiling or a floor, close the stop tap and keep away from wet light fittings and sockets. Then ring us with your notes, because they save time on the visit.
If an insurer may be paying, the policy wording comes first. Look for the words trace and access: not every home policy has them, and some insurers ask to agree the work before anyone starts. You get the written report, with the location, methods, readings and photographs, once the bill for the visit is cleared in full. The insurer alone decides whether a claim is paid.
Some leaks on a home's supply pipes qualify for no find, no fee on home water leaks; full conditions are on our terms page. It does not cover central heating, shared mains, businesses or leaks that come and go. If you only hear the sound now and then, it may be one of those, so note the times before you ring.