To find a water leak underground, first read the signs: a patch of lawn or drive that stays wet, greener grass, low pressure or a creeping bill. Then confirm it with the meter test. Turn everything off, and if the meter still moves, water is escaping. Pinpointing the exact spot under ground reliably needs professional acoustic, thermal and tracer-gas equipment.
An underground leak is the sneakiest kind. There is no dripping tap and no damp ceiling, just a buried pipe quietly losing water, often for months, while your bill climbs and the ground above gives nothing away. The good news is that you can confirm one yourself with a couple of simple checks, and narrow down roughly where it is, before anyone lifts a slab. Here is how to spot the signs, prove the leak with your meter, and know when it is time to bring in a specialist.
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Signs you have an underground water leak
Because the pipe is buried, you read the symptoms above ground rather than the leak itself. Any one of these on its own might be nothing; two or three together is a strong hint that water is escaping below the surface.
- A patch that stays wet or soft. A section of lawn, border or drive that is boggy or spongy underfoot when the rest is dry, and stays that way through a dry spell, is the classic sign.
- Greener, faster-growing grass. A constant trickle of water acts like a sprinkler, so the grass over a leak is often lusher or longer than everything around it.
- A drop in water pressure. If the pressure falls across the house, water may be escaping from the supply before it reaches your taps.
- The sound of running water. A faint hiss or trickle when every tap is off, especially near where the supply enters the house, is worth investigating.
- An unexplained rise in your bill or a meter that keeps ticking over with nothing in use (more on that below).
- Cracked or sunken paving. Escaping water washes away the ground beneath a path, drive or patio, so new cracks, dips or lifted slabs can sit directly over a leak.
One thing to keep in mind: the wet patch is not the leak. Water follows the easiest path through soil and along the pipe trench, so it can surface a long way from the actual break, anywhere from a few metres to more than thirty. That is exactly why digging where the ground looks wettest so often misses.
The water meter test: confirm it in an hour
Surface signs point to a leak; the meter proves it. This is the single most useful check you can do yourself, and it costs nothing.
- Turn everything off. Close all taps, switch off the washing machine and dishwasher, and make sure no toilet is refilling. Even a slow trickle from a worn flush valve will throw the test off.
- Read the meter and write the figure down, or note the position of the dial.
- Wait one to two hours without using any water at all.
- Read it again. If the reading has moved with nothing in use, water is escaping somewhere on your supply.
Water companies recommend this exact method. Wessex Water and Southern Water both publish versions of it. A meter that moves with the house shut down is about as clear a confirmation of a hidden leak as you will get.
Narrowing down where the leak is
Once the meter confirms a leak, you can work out roughly where it is with one more step: isolating your internal stop tap (usually under the kitchen sink).
- Turn the internal stop tap off and repeat the meter test.
- If the meter stops moving, the leak is inside the house, on the pipework beyond the stop tap.
- If the meter keeps moving with the internal stop tap closed, the leak is on the buried supply pipe between the boundary and the house. That is an underground leak.
This is the same logic water suppliers use to point homeowners in the right direction. It will not tell you the precise spot, because for that you need detection equipment, but it tells you whether you are dealing with an internal problem or a genuine underground one. If your leak sits on the run between the boundary and the wall, our guide to a water leak between the meter and the house covers that stretch in detail.
Where DIY ends and equipment begins
You have now done the valuable part yourself: you have confirmed a leak and established it is underground. What you cannot do safely or accurately with household tools is pinpoint it. Digging "near the wet bit" risks cutting the wrong pipe, damaging a drive or patio for nothing, and still missing the leak that has tracked metres away underground.
If the leak is under a solid indoor floor rather than the garden, the same limits apply but the stakes are higher, so our guide to finding a leak under a concrete floor is worth a read before you lift any flooring. If your goal is simply to map where your pipes run before any work, rather than to find a leak, that is a different job. Our piece on how to locate water pipes underground explains tracing intact pipe routes. To find the leak itself without excavation, the reliable answer is professional detection.
How a specialist pinpoints it
Professional underground water leak detection finds the exact point of escape without digging up the garden, by combining several non-invasive methods:
| Method | How it finds the leak |
|---|---|
| Acoustic detection | Sensitive ground microphones pick up the distinctive hiss of pressurised water escaping a buried pipe, even under concrete or tarmac. |
| Thermal imaging | A leak changes the temperature of the surrounding ground or floor; a thermal camera shows the cooler or warmer trail the eye cannot see. |
| Tracer gas | A safe gas mix is introduced into the isolated pipe. It rises through the ground at the leak and is picked up by a detector at the surface, which works well for very small or deep leaks. |
Used together, these methods cross-check each other and let us mark a leak to within a small area before anyone breaks ground. That is the whole point: find first, dig once, repair the minimum. For the wider toolkit on supply lines specifically, see our overview of the methods used to detect leaks in mains water supply lines. The same non-invasive approach runs through all of our water leak detection work.
Whose pipe is it? UK responsibility
Before you spend money finding and fixing an underground leak, it helps to know whose pipe it is. As a general rule in the UK:
- The supply pipe running from the boundary of your property into the house, plus all the pipework inside, is the homeowner's responsibility.
- The pipes up to the boundary (the communication pipe and the main) are the water company's responsibility.
- The boundary stop tap usually marks the dividing line between the two.
This split is set out by Ofwat and confirmed by water suppliers and the consumer body CCW. There are local exceptions, so if you are unsure, check with your water company. If South West Water has contacted you about high usage, our guide on what to do when South West Water says you have a leak walks through your options, including the leak allowance many suppliers offer to refund some of the lost water once the leak is repaired.
Underground leaks in Cornwall & Devon
Across Cornwall and Devon we trace buried supply-pipe leaks every week, under lawns, driveways, patios and solid floors, using acoustic, thermal and tracer-gas equipment so we find the leak with the least possible disruption. If your meter is moving with the house shut down, or you have a patch of ground that never dries out, you have done the hard part already. The next step is locating it precisely, and that is exactly what we do, fast and without tearing up the garden on a guess.
Frequently asked questions
What are the first signs of an underground water leak?
The usual early signs are a patch of ground that stays wet or soft when the rest is dry, grass that is greener or growing faster in one spot, a drop in water pressure, the sound of running water with no tap on, and an unexplained rise in your bill or a meter that keeps ticking over when everything is off.
How do I confirm a leak with my water meter?
Turn off every tap and water-using appliance, make sure the toilet is not refilling, then read the meter. Wait an hour or two without using any water and read it again. If the reading has moved with nothing in use, water is escaping somewhere on your supply. On a buried pipe, that usually means an underground leak.
Can I find an underground water leak myself?
You can confirm you have one and roughly where it is, using the meter test and surface signs such as a wet patch or sunken paving. Pinpointing the exact spot under a lawn, drive or floor reliably needs acoustic, thermal and tracer-gas equipment. That is why most homeowners confirm the leak themselves and then call a specialist to locate it without digging up the whole garden.
Who is responsible for an underground water leak in the UK?
As a general rule the supply pipe running from the boundary into your home, and all the pipework inside, are the homeowner's responsibility, while the pipes up to the boundary are the water company's. The boundary stop tap usually marks the dividing line. Check with your water company if you are unsure, as there are local exceptions.
How far can an underground leak travel from the actual pipe?
Water from a buried leak can travel a long way before it surfaces. It follows the easiest path through the ground, so the distance can run from a few metres to more than thirty. That is why the wet patch you can see is often nowhere near the real break, and why guessing where to dig so often misses.
Will I lose money on water I cannot even see?
Yes. A buried leak runs continuously, day and night, and every litre passes through your meter, so a metered home pays for all of it until the leak is found and fixed. Many UK water companies, including South West Water, offer a leak allowance that can refund some of the loss once the leak is repaired, so it is worth asking.
Got a leak you can't see? We'll find it without digging up your garden
We pinpoint underground water leaks across Cornwall & Devon with acoustic, thermal and tracer-gas equipment. Fast response, minimal damage, and we never guess about where to dig.
Call Dickie on 07822 025 911 No Find, No Fee on residential leak detection (subject to terms)