How To Tell If You Have A Water Leak Underground
Nov 20, 2025
It’s easy to miss an underground leak (until the signs start stacking up!).
Maybe it’s a jump in your water bill, soft ground underfoot, or that faint sound of running water when everything’s switched off. These leaks don’t announce themselves, but they can quietly cause serious damage if left unchecked.
We’ll explain how to tell if you have a water leak underground, the signs to watch for, and what to do next.
Key Notes
Unexplained bill spikes, soggy patches, and pressure drops signal underground leaks early.
DIY meter test: turn off all water and check if the meter moves.
Modern detection uses acoustic sensors, thermal imaging, and tracer gas – no digging required.
Professional detection takes 1-4 hours and provides insurer-approved reports with the exact location.
Early Warning Signs You Might Have an Underground Leak
The biggest challenge with underground leaks is that they often start small and stay hidden.
Here’s what to look for:
1. Unexplained Increase in Water Bills
If your water bill suddenly climbs without any increase in usage, that’s a red flag. Continuous leaks underground can waste water around the clock.
2. Soggy or Lush Patches in the Garden
Uneven moisture or grass that looks healthier in isolated spots can indicate a leak below feeding that area.
3. Drop in Water Pressure
When water escapes underground, the pressure to your taps and showers drops noticeably.
4. Cracks in Driveway or Foundation
Constant moisture can erode soil and shift foundations, leading to new cracks or widening existing ones.
5. Pooling Water or Unexplained Puddles
Water bubbling up or pooling without recent rainfall often points to a broken pipe below the surface.
6. Sounds of Running or Hissing Water
Hearing water movement when all taps are off? That could be water escaping from underground pipes.
7. Musty Smells or Mould Indoors
Persistent dampness caused by underground leaks can trigger mould and unpleasant odours in basements or lower levels.
8. Depressions or Sinkholes
Ongoing water flow erodes soil, sometimes forming soft patches or minor sinkholes in gardens.
9. Overgrown or Unusually Lush Grass Patches
Extra moisture in one spot can make the vegetation thrive unnaturally compared to the rest of your lawn.
Spotting even one or two of these signs early could save you a huge headache (and bill) later on.
Simple Ways to Confirm a Leak Before Calling a Professional
If you suspect a leak but aren’t sure, try these basic DIY checks before calling in help:
Water Meter Test. Turn off all taps and water-using appliances, then check your water meter. If it’s still moving after 30 minutes or more, water is escaping somewhere.
Toilet Dye Test. Drop a few food colouring drops into your toilet cistern. If the colour shows up in the bowl without flushing, your toilet’s leaking – a common hidden culprit.
Listen and Observe. Stand quietly near suspect areas indoors and outside. Faint hissing or dripping could mean a pressurised pipe is leaking beneath.
Check Outdoors. Look for overly damp patches or puddles in dry weather, particularly near water mains or meter boxes.
These simple tests can help confirm that something’s wrong, but they won’t pinpoint where the leak is. For that, professional detection is key.
How Professionals Detect Underground Leaks (Without Digging)
Modern leak detection is all about precision and minimal disruption. Today’s technology allows specialists to locate leaks to within inches – often without touching a shovel.
Here’s how:
Acoustic Leak Detection
Using sensitive microphones placed along the suspected route of your pipe, technicians listen for the distinct sound of water escaping under pressure. These sounds are amplified and analysed to identify the exact location.
Ultrasonic Detection
Ultrasonic sensors detect high-frequency sounds that leaks produce – ideal for noisy environments or where water pressure is variable.
Thermal Imaging Cameras
Thermal cameras identify temperature differences in soil or concrete caused by leaking water. This helps find leaks beneath floors or driveways with no need for excavation.
Tracer Gas Detection
A harmless, odourless gas (often hydrogen and nitrogen) is introduced into your pipe system. The gas escapes where the leak is and rises through the ground, detected by specialised sensors above.
Ground Penetrating Radar (GPR)
GPR sends radar waves underground to detect changes in density and moisture, revealing exactly where the leak is disrupting the soil structure.
Leak Noise Correlation
For larger systems, multiple sensors are placed along a pipeline. By comparing how long it takes leak noise to reach each sensor, technicians calculate the precise location mathematically.
Borescope Cameras & Moisture Meters
These tools visually confirm leaks or measure dampness levels to support findings from other methods.
Detecting Leaks Beneath Concrete or Hard Surfaces
Leaks under slabs, tarmac, or foundations are trickier but absolutely possible to detect without damage.
Professionals use:
Thermal imaging to highlight temperature changes beneath the surface.
Acoustic microphones to listen for the faint hiss of escaping water through concrete.
Tracer gas detection for pinpoint accuracy in solid surfaces where sound can’t travel effectively.
These techniques mean no unnecessary drilling or guesswork – just clear answers before any repair begins.
What to Expect During a Professional Leak Detection Visit
A typical inspection usually takes one to four hours, depending on the property size and complexity.
Here’s what happens:
Initial Assessment: The technician discusses your symptoms and performs a quick visual inspection and water meter check.
Non-Invasive Testing: Using acoustic, thermal, or tracer gas methods to locate leaks accurately.
Data Analysis & Confirmation: Signals are interpreted, cross-checked, and refined until the exact spot is identified.
Marking & Reporting: The technician marks the leak location and provides an insurer-approved report complete with photos and recommendations.
The process is clean, efficient, and designed to minimise any disruption to your property.
When to Call a Professional Leak Detection Service
If you’ve noticed several warning signs or your own tests suggest an ongoing leak, it’s time to call in professionals.
You should also reach out if:
The suspected leak is under concrete or hard surfaces.
You need insurance claim documentation.
The problem keeps recurring despite previous repairs.
You want to confirm the issue without unnecessary damage or digging.
Professional detection services save you time, stress, and money by pinpointing leaks precisely the first time.
Need Certainty Without Tearing Up Floors?
No find, no fee & same-day availability.
Frequently Asked Questions
Can an underground water leak fix itself?
Unfortunately, no. Leaks only get worse over time as pressure, corrosion, or soil movement expand the damaged area. Even a slow leak can eventually cause significant structural and water damage if ignored.
How much does professional underground leak detection cost in London?
At London Leak Detection, our fixed rate is £490 (4 hours + VAT) with a No Find, No Fee Guarantee – meaning you only pay if we locate the leak. Competitors often charge £595+ for just 3 hours with hidden extras.
Do I need to excavate to repair an underground leak?
Not always. With precise detection, only the affected area needs to be accessed. Non-invasive methods minimise disruption and save you from unnecessary digging or guesswork.
Will my home insurance cover underground leak detection?
Most UK home insurance policies do cover leak detection and repair if the leak has caused damage. Our detailed, insurer-approved reports help streamline your claim and maximise coverage.
Conclusion
Underground leaks rarely shout for attention. A higher bill here, a soggy patch there, a bit of mould that won’t clear up. Knowing how to tell if you have a water leak underground can save you from those slow, silent problems turning into structural damage or soaring costs.
Today’s non-invasive detection methods can find leaks with pinpoint accuracy, even beneath concrete, without tearing anything up.
If you’ve spotted a few signs that don’t sit right, don’t wait for proof in the form of damage. Get a free quote for professional leak detection that finds the problem fast and keeps your property protected.
