Do this first
- Do the test properly once, rather than roughly three times. Turn off every tap, the washing machine, the dishwasher, any water softener and the ice maker. Ask everyone not to flush. Then photograph the meter face, including the small sweep dial, with the time visible.
- Wait at least thirty minutes, using nothing, and photograph it again. Two hours overnight is better still, because nothing masks a slow leak like somebody rinsing a cup.
- Now isolate the house. Close your internal stopcock, wait, and read the meter a third time.
- Read the result. Still turning with the stopcock shut means the leak is outside the house on the buried supply pipe between the meter and the building. Stopped when the stopcock closed means the leak is inside.
- Check the obvious internal culprits before anything else: put a few drops of food colouring in each WC cistern and leave it twenty minutes without flushing. Colour in the pan means that toilet is running away silently, and a passing WC valve is the most common cause of a moving meter by a distance.
- If the ground outside is soft, green in a dry spell, or sinking, do not dig. Photograph it and note where it is relative to the boundary.
Inside, outside, or not yours at all
The stopcock test splits this into three cases with three different owners, and getting it wrong is expensive because one of them involves excavation.
| Result | Where the leak is | Whose problem |
|---|---|---|
| Meter stops when the internal stopcock is closed | Internal plumbing: WC valve, a weeping joint, a heating fill loop, an appliance hose | Yours |
| Meter keeps turning with the internal stopcock closed | The buried supply pipe between the boundary and the house | Yours as the homeowner |
| Wet ground or a sinking pavement on the street side of the boundary | The water main or the communication pipe | The water company |
The boundary is the line that matters. Thames Water is responsible for the mains and for the communication pipe that links your supply pipe to the main; the supply pipe running from the boundary of your property into your home is the homeowner's. A shared supply serving several properties is the joint responsibility of all the owners connected to it, which is common in converted London terraces and worth establishing before anyone commits to a repair.
Two internal cases account for most moving meters. A WC fill or flush valve passing into the pan runs continuously and silently, and the dye test finds it in twenty minutes. A heating filling loop left slightly open bleeds mains water into the sealed system around the clock, which also explains a boiler pressure that never seems to fall. If the meter is turning and the toilet is trickling into the pan, start there before anything else.
What the repair involves
Internally, the leak is traced with acoustic listening on the pressurised pipework and moisture mapping through walls and floors, then cut out and remade. Externally, a supply pipe leak is located before anything is dug: acoustic correlation along the run, ground microphone over the suspected point, and tracer gas into a drained pipe where the ground is noisy or the pipe is deep. That is what turns a trench across a garden into a single small excavation.
The repair is a cut-out and remake in MDPE, or a full pipe replacement where the existing run is old lead, galvanised steel or perished alkathene and patching it simply moves the next failure along a few metres. Then the reinstatement: backfill, compaction, and paving, path or lawn put back. Mains supply pipe repair covers that whole sequence, and there is more on the boundary question in our Thames Water hub.
When it is not us
- The dye test turns the pan blue. Fit a new fill or flush valve. It is an inexpensive part and a job many people do themselves.
- The filling loop was open. Close both ends and detach it. Nothing else is wrong.
- Water is surfacing on the street side of your boundary, or the stop tap chamber in the pavement is full. Report it to your water company. That is their pipe and their cost.
- You want the bill adjusted. Once the leak has been repaired you can apply for a leak allowance, and there are conditions attached to how quickly the repair is done. Our water bills hub sets out the evidence to keep.
- You have had a repair notice from the water company. Read it before booking anyone, because it carries a deadline you can be held to.
- You rent. Pass it to the landlord. The supply installation is theirs to keep in repair, and so is the bill for fixing it.