Signs of a supply pipe leak
Most of these leaks are silent, invisible and months old by the time anyone notices. The evidence usually arrives on a bill rather than on the ground.
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A supply pipe runs below the frost line, often under a drive or a lawn, and the ground around it is usually good at taking water away. On sand or gravel a leak can run for a year with nothing showing at the surface at all.
That is why the list below is worth reading properly. Several of the strongest signs are things people notice and dismiss, and two of them appear nowhere near the fault.
Outside the house
| Sign | What it means |
|---|---|
| A patch of ground that never dries out | Water surfacing along the path of least resistance, which is rarely directly above the fault. On a slope it can appear several metres downhill. |
| One strip of lawn greener or growing faster than the rest | The line of the pipe, fed from below. It often shows in a dry spell before anything becomes visibly wet. |
| Block paving or slabs that have started to sink or rock | Fines being washed out of the bedding under the surface. This is the point at which the leak starts costing more than the water. |
| A drain or a gully running clear when it has not rained | Escaping mains water finding a route into the drainage system. Clean, continuous flow with nobody using the property is the giveaway. |
| Hissing at the boundary chamber or the outside stop tap | Water forcing through a small opening under pressure. Worth listening for at night, when traffic and appliances are quiet. |
| Frost or a bare patch in winter where snow lies everywhere else | Mains water moving underground keeps the ground above it slightly warmer. |
Inside the house
| Sign | What it means |
|---|---|
| The meter turning with every tap off | The strongest evidence there is. Nothing in an unoccupied house moves a meter except a leak. |
| Low pressure at the kitchen cold tap | Water escaping before it reaches the house. Check the stop tap is fully open first, because a half closed one behaves identically. |
| Damp at the base of an internal wall near where the pipe enters | The supply pipe entering through or under the wall, leaking at the point it comes in. |
| A cold patch on a solid floor | Mains water spreading under the screed. This is the one thermal imaging reads best. |
| A water softener getting through salt faster than usual | More water passing through the system than the household is actually using. |
| A bill or a letter you were not expecting | Either your own consumption figures or your water company’s network monitoring. Both are measurements, and both are worth acting on. |
The symptoms that point somewhere else
Half the value of a survey is ruling things out. These five are regularly reported as supply pipe leaks and almost never are.
- Damp that appears only after heavy rain. Groundwater or surface water. Mains water does not care what the weather is doing.
- A wet patch that dries out between uses. Waste or drainage, fed in bursts when somebody uses the property.
- A smell with the water. Drainage. Mains water has no smell.
- Pressure that drops only at certain times of day. Demand on the public network, or a pressure reducing valve doing its job.
- Water appearing after somebody has a shower. Internal plumbing or a waste connection, not the buried supply.
Questions about the evidence
How can I check whether the supply pipe is leaking?
If your meter is outside, turn off taps and water using appliances. Close the internal stop tap gently, record the meter reading, wait 30 minutes without using water, then read it again. Do not force a stiff valve.
A rising reading suggests water is escaping or being used between the meter and the closed valve. A faulty valve, shared supply or another branch can complicate the result. An unchanged reading does not rule out an intermittent leak. Ask for help if the meter or valve is inaccessible.
Guidance: Thames Water household leakage guidance; ADI Liverpool investigation.
Can I have a leak without a wet patch or a high bill?
Yes. A hidden leak may not produce a visible wet patch. If you are not billed by a meter, extra water loss will not show as increased usage on your bill. Persistent damp ground or unexplained pipe noise can be reasons to investigate, but neither proves a supply pipe leak.
With a metered bill, check the readings and any change in household use as well as looking for leaks.
Guidance: ADI water mains service; Scottish Water customer leakage guidance.
Does low water pressure mean there is a leak?
A leak is one possible cause. Partly closed valves, restricted pipework or a problem on the public network can also reduce pressure or flow. Check your supplier’s service updates and ask them for advice if the cause is unclear.
Guidance: Ofwat water pressure guidance.
Describe what you are seeing
Tell us what the meter is doing, what the ground looks like and whether the stop tap shuts properly. That is usually enough to say whether it sounds like the supply pipe. Seven days a week, 7am to 9pm.
The office team speak to every customer before an engineer is booked, and the engineer who attends is the one who writes the report.
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