Grange PlumbingUnderground water leaks are sneaky. The pipe is buried under your lawn, drive or patio, so by the time there's visible evidence something is usually already wrong. The good news is that a leaking supply pipe almost always leaves clues if you know what to look for. Here are the seven signs I see most often on jobs across Sussex, plus what to do about each one.
1. A water bill that keeps climbing
Short answer
A steadily rising water bill with no change in how much water you actually use is one of the clearest early signs of an underground leak.
If your household habits haven't changed but your bill has crept up quarter after quarter, an underground leak is one of the most likely explanations. A pinhole leak on a supply pipe can waste hundreds of litres a day without ever reaching the surface. Compare your last few bills, and if usage is trending up for no obvious reason, it's worth booking a leak detection survey.
2. The meter keeps turning with everything off
Short answer
Turn everything off, note the meter reading, wait half an hour and check again. If it's moved, you have a leak on your side of the boundary.
This is the simplest DIY test there is. Turn off every tap and appliance in the house, then close your internal stop tap. Note the meter reading, wait 30 minutes without using any water, then check it again. If the digits have moved, water is escaping somewhere between the meter and your stop tap — almost always the supply pipe.
Whose pipe is it?
Not sure whether the fault is yours or the water company's? Our guide on <a href="/blog/who-is-responsible-for-water-supply-pipe-leak">who is responsible for a leaking water supply pipe</a> explains exactly where the boundary sits.
3. A patch of lawn that's always green, wet or sunken
Short answer
An unusually green, boggy or sunken patch of lawn — even in dry weather — often sits directly above or along the route of a leaking supply pipe.
Water tracks along the line of least resistance, so a leak often surfaces well away from the actual fault — but it does tend to surface. Look for a stretch of grass that's noticeably greener and lusher than the rest, ground that never quite dries out even in a heatwave, or a slight dip where the soil has been washed away underneath.
4. Low or dropping water pressure
Short answer
Falling water pressure across the whole house — not just one tap — points towards a leak on the incoming supply pipe rather than internal plumbing.
A supply pipe leak reduces the volume of water actually reaching your taps, so pressure throughout the house can fall gradually over weeks or drop suddenly overnight. If every tap in the house is affected rather than just one fixture, suspect the incoming supply rather than internal pipework.
5. The sound of running water with everything off
Short answer
Running water noises with all taps and appliances off almost always mean an active leak somewhere in the pipework.
If you can hear water running or trickling somewhere underground or behind a wall when every tap and appliance is switched off, take it seriously. It's one of the most reliable signs of an active leak, and it's worth acting on quickly before the ground around the pipe washes away further.
6. Cracked, sunken or sinking paving and driveways
Short answer
Sunken, cracked or dipping paving and driveways are usually a sign that an underground leak has been running for weeks or months, washing away the ground beneath.
Water escaping underground gradually erodes the surrounding soil, and eventually the surface above it — block paving, tarmac or concrete — starts to dip, crack or subside. This is usually a sign the leak has been running for some time. See our case study of a steel supply pipe leak under a Sussex driveway for a real example of how far this can progress before it's caught.
7. Damp patches inside the house near the pipe's entry point
Short answer
Damp or musty patches on internal walls or floors near where the supply pipe enters the house suggest the leak is close to the building and needs urgent attention.
If the leak is close to where the supply pipe enters the building, you may see damp patches on internal walls or floors near that point, sometimes with a musty smell. This is one of the later-stage signs and usually means the leak needs attention quickly to avoid structural damage.
What to do if you spot any of these signs
Short answer
Test the meter yourself, then book a non-invasive leak detection survey. Repairs or trenchless moling replacement can usually follow within a day or two once the leak is located.
Start with the meter test above, then get a proper leak detection survey using acoustic and thermal equipment so the leak can be pinpointed without unnecessary digging. Depending on the pipe's age and condition, the fix will either be a targeted repair or a full replacement using trenchless moling, which avoids trenching across your whole garden or drive. If you'd like an idea of cost before booking a survey, our water main replacement cost guide sets out typical 2026 UK prices.
Key takeaways
- A rising water bill with no change in usage is the most common early sign.
- A patch of lawn that's always green or waterlogged usually sits above the leak.
- A meter that keeps turning with every tap off confirms a leak somewhere on your supply.
- Sunken paving or a sinkhole means water has been washing away the ground for some time.
- Non-invasive leak detection finds the exact spot before any digging starts.
- Trenchless moling repairs or replaces the pipe without trenching across the whole garden.
Frequently Asked Questions
How do I know if I have an underground water leak?
Check for a rising water bill, low pressure, a patch of lawn that's always wet or green, the sound of running water with taps off, or sunken paving. The meter test — turn everything off and watch whether the dial still moves — is the quickest way to confirm it.
Can an underground leak damage my house?
Yes. Left long enough, an underground leak can undermine foundations, sink driveways and paths, and cause damp inside the property near the pipe's entry point. Acting early keeps the repair small.
How much water can a small underground leak waste?
Even a modest pinhole leak can waste several hundred litres a day, which adds up to thousands of litres — and a noticeably higher bill — over just a few weeks.
Do I need to dig up my whole garden to find a leak?
No. Professional leak detection uses acoustic correlation and thermal imaging to pinpoint the leak to within a metre or so, so only a small area needs to be opened up.
Is it my leak or the water company's?
It depends where the leak sits relative to your property boundary. See our guide on who is responsible for a leaking water supply pipe for how to tell.
What's the fix once the leak is found?
A modern plastic pipe with a single fault is usually repaired. Older lead or steel pipe, or a pipe with a history of repairs, is normally better replaced using trenchless moling, which installs a new water main without digging a trench.
More guides from Grange Plumbing
- Does Home Insurance Cover Trace and Access?
- How to Tell If Your Home Has Lead Water Pipes
- Underground Water Leaks: The Hidden Signs Every UK Homeowner Should Know
- Burst Water Main? What to Do in the First 10 Minutes
- Water Main Replacement Cost UK — 2026 Guide
- What Is Moling and Why Is It Better Than Digging?
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