Water Leak Under a Driveway: Signs and What to Do
Reviewed by the Devon Leak Detection team. Last updated June 2026
The short answer
A supply-pipe leak under a driveway usually shows up as an unexplained damp or lush patch, falling pressure, a higher water bill or a meter that keeps ticking with everything off. Digging blindly is costly. Acoustic and tracer-gas detection pinpoint the leak first, so any excavation is small and targeted.
A driveway leak is one of the trickier problems a homeowner can face. The pipe runs out of sight, often under concrete, block paving or tarmac, and the first hint that something is wrong is rarely a dramatic burst. More often it is a slow escape that quietly drives up your bill for weeks before you notice. The good news is that the warning signs are fairly consistent, and once you know what to look for you can act early, before the leak undermines the surface or wastes a fortune in water.
This guide walks through the signs of a buried supply-pipe leak under a drive, why guessing at the location and digging is a costly mistake, and how non-invasive detection finds the exact spot before a spade ever touches the ground.
How the supply pipe under your drive works
The pipe carrying mains water into your home is called the supply pipe. It runs from the boundary of your property, under whatever sits on top of it, including your driveway, garden or path, and into the house. In most Devon homes that boundary is marked by an external stop tap, often set in a small chamber near the pavement edge.
Where that boundary sits matters, because it usually decides who pays. The water company looks after the pipework on its side, out in the public land and the main itself. The section that crosses your property, including the part buried under the drive, is generally the homeowner’s responsibility to find and repair. South West Water can confirm the exact boundary for your address if you are unsure. Many older supply pipes are made of materials that corrode or crack over time, and ground movement, tree roots and the weight of vehicles overhead all add stress, which is why driveways are such a common place for these leaks to appear.
Signs of a water leak under your driveway
Because the pipe is hidden, the clues tend to show on the surface or in your bills rather than as an obvious puddle. A single sign on its own might be nothing, but two or three together are a strong hint that water is escaping underground.
Signs you might notice:
- A damp patch or area of standing water on the drive that lingers even in dry weather
- An unusually green or fast-growing patch of grass or weeds near the pipe run
- A drop in water pressure at the taps, particularly when more than one is running
- A water bill that has crept up with no change in how much you use
- A meter that keeps ticking over after you have turned everything off inside
- The faint sound of running water near the external stop tap
- Soft, sunken or cracking sections of the driveway surface
The meter test you can do today
If you have a water meter, there is a simple check that points firmly towards a hidden leak. Turn off every tap and water-using appliance in the house, then read the meter and note the figures. Leave it for an hour or two without using any water, then read it again. If the numbers have moved, water is leaving the system somewhere, and if everything inside is genuinely off, that somewhere is often the buried supply pipe.
This test will not tell you where the leak is, only that one almost certainly exists. Locating it under a solid drive is a separate job, and that is where the temptation to dig becomes a problem.
Why digging blindly is a costly mistake
When a leak is somewhere under a drive, the instinct is to start digging where the water shows. Unfortunately, water rarely surfaces directly above the leak. It travels along the line of least resistance, following the pipe trench, the edge of a slab or a layer of harder ground, and can emerge several metres from the actual fault. Dig at the wet patch and you may find perfectly sound pipe.
That is an expensive way to learn the lesson. Lifting block paving, breaking out concrete or cutting tarmac is disruptive and the reinstatement is rarely cheap or invisible. If the first hole misses, the second and third add up fast, and your driveway ends up looking patched. Excavating without knowing the exact location also risks clipping other buried services, such as gas, electricity or drainage, which turns one problem into several.
The sensible order is the other way round. Find the leak precisely first, then dig once, in the right place, with a small opening.
How non-invasive leak detection finds the spot
Professional detection pinpoints a buried leak without tearing up the drive to look for it. Two methods do most of the work, and they complement each other well.
Acoustic detection. Water escaping from a pressurised pipe makes a noise, a hiss or rush where it forces through the split and a knock where it strikes the surrounding ground. Sensitive ground microphones and listening sticks pick up these sounds at the surface. By comparing the volume at different points, the leak can be traced to a small area without any digging at all.
Tracer gas. When a leak is very small, or the surface deadens the sound, a safe tracer gas comes into its own. A blend that is typically around 95 percent nitrogen and 5 percent hydrogen is introduced into the isolated pipe. The hydrogen is the lightest gas there is, so it rises straight up through the ground and surfaces directly above the leak, where a sensitive detector picks it up. The mix is non-toxic and non-corrosive, which makes it suitable for use with drinking-water pipes.
Used together, acoustic equipment and tracer gas usually narrow a leak under a drive down to a small, well-defined spot. That means any excavation is limited to a single, targeted opening rather than a fishing expedition across the whole driveway. You can read more about how we approach buried pipes on our underground water leak detection page.
What to do if you suspect a leak
If the signs above ring true, start by doing the meter test to confirm water is being lost. It is worth knowing where your internal stopcock is, usually under the kitchen sink or where the pipe enters the house, so you can shut the supply off quickly if you ever need to. It is also worth a call to South West Water, who can confirm the boundary for your property and explain any support they offer towards finding or repairing a leak on a private supply pipe.
Beyond that, the most useful step is to have the leak located accurately before any work begins. Pinpoint detection protects your driveway, keeps the repair small and gives you a clear answer rather than a guess. We cover homes right across the county, so if you want a steer on next steps, see what we do across Devon or browse more guides in our articles.
Frequently Asked Questions
Turn off every tap and appliance, then watch the meter for an hour or two. If it still moves with everything off inside, water is escaping outside the house, often along the buried supply pipe. Damp patches, lush grass or sinking on the drive point the same way.
The supply pipe crossing your property, including the part under the drive, is generally the homeowner’s responsibility to find and repair. The water company looks after its side of the boundary. South West Water can confirm exactly where that boundary falls for your address.
No. The aim of pinpoint detection is to avoid exactly that. Acoustic equipment and tracer gas narrow the leak to a small spot, so any excavation can be a single, targeted opening rather than digging across the whole surface guessing where it is.
Yes. The tracer mix is typically around 95 percent nitrogen and 5 percent hydrogen. It is non-toxic and non-corrosive, which makes it suitable for use with drinking-water supply pipes. The hydrogen simply rises through the ground and surfaces above the leak.
Water follows the easiest path underground, running along the pipe trench or a harder layer of ground before surfacing. It can emerge several metres from the actual fault, which is exactly why digging at the wet patch so often misses and proper detection is worth doing first.
Trace the leak before you lift a single slab
Talk to the Devon Leak Detection team for a fast response and a precise answer, with no needless digging.