A wet patch in the garden that stays soggy through dry weather, especially with greener, faster-growing grass over it, often points to a leaking buried supply pipe. First rule out a spring, a blocked drain or a misdirected downpipe. Then do the water meter test with everything off. If the meter moves, the leak is on your side.
The rest of the lawn dried out days ago. One patch near the path is still spongy underfoot, and now you look at it, the grass there has been thicker and greener since spring. Or water keeps seeping between the slabs on the drive with no rain to explain it. In Cornwall there are several honest explanations for wet ground, and only one of them is coming out of your water bill. This guide takes them in order, gives you the meter test that settles the question, explains who pays for what once the leak is confirmed, and describes how a buried leak is located without digging up the garden to look for it.
Why a buried leak shows as a wet patch
Your supply pipe runs under the garden from the boundary stop valve to the stopcock inside, carrying mains water under constant pressure every hour of the day. If it develops a crack, a pinhole or a loose joint, water escapes steadily. It does not gush. It soaks into the ground around the pipe and takes the easiest route, which on most plots is back up to the surface somewhere close to the fault. Treated water arriving all day long is a gift to the grass above, which is why the patch is often greener and grows faster than its neighbours, and why it stays wet when everything else has dried.
Buried pipes fail for ordinary reasons. Old galvanised iron or lead pipe corroding through, a compression joint working loose with ground movement, frost heave over a hard winter, a tree root wrapping round a fitting, or a spade going through it years ago and being patched badly. Long private pipes on farms and rural properties around Bodmin Moor have more length to fail and more of it under fields nobody looks at.
Rule out the innocent explanations first
A leak is relentless. The test for every other cause is whether the wet patch persists when that cause is removed.
- Rain and lie of the land. Give it several dry days. Low spots and heavy clay hold water longest, so compare the patch with similar ground nearby rather than the whole lawn.
- A spring or high water table. Much of Cornwall sits on clay over shale or granite, and springs are common on slopes. A spring patch is usually cold, often on a hillside, tends to be wetter in winter and after rain, and the water is clear and tastes of nothing. It also predates you. Ask a neighbour who has been there a while.
- A land drain or soakaway. A blocked or collapsed field drain, or a soakaway that has silted up, keeps ground boggy long after rain. Look for old clay pipe ends in the bank or a manhole nearby.
- A downpipe, gutter or water butt. A rainwater outlet discharging into that corner mimics a leak surprisingly well. Check where each downpipe goes and whether a butt overflow is aimed at the patch.
- A drain or waste pipe. If the ground stays wet near an inspection chamber or a soil pipe, or there is a smell, you may have a foul drain fault rather than a clean-water leak. That is a drainage job and needs a different approach.
- Irrigation or an outside tap. A buried irrigation line, a hose left connected and weeping at the tap, or a pond liner failing all feed the ground without touching the mains supply. Turn them off and wait.
If the patch stays wet with all of those removed, a supply pipe leak moves to the top of the list, and the meter test confirms it.
The water meter test
Most Cornish homes are metered, and the meter is the cheapest leak detector you own. It usually sits in a chamber under a small cover at the boundary, near the pavement or at the end of the drive. Do this on a dry day.
- Turn everything off. Every tap, the washing machine, the dishwasher, the garden hose. Ask the household not to flush for an hour.
- Read the meter. Lift the lid and note the full reading, including the small red dials or the last digits. Some meters have a small leak indicator wheel that turns with any flow.
- Wait at least half an hour, ideally longer. Then read it again.
- Now close the internal stopcock and repeat. This is the step that tells you where the leak is. If the meter still moves with the house isolated, the leak is on the supply pipe between the meter and the house, under your garden. If it stops when the stopcock is closed, the leak is inside.
A meter that does not move at all with everything off means the leak is probably not on the mains side, and a wet patch is more likely a spring, a drain or a rainwater problem. Our guide on a water meter moving when nothing is on goes through the reading in more detail, and whether a leak is before or after the water meter explains what the position means for who pays.
| What you notice | Most likely cause | What to do |
|---|---|---|
| Wet patch, greener grass, meter moves with stopcock closed | Supply pipe leak on your side | Book underground leak detection, contact South West Water about a leak allowance |
| Wet patch, meter still with stopcock closed, moves with it open | Leak inside the house feeding the ground | Internal leak detection survey |
| Wet patch, meter does not move at all | Spring, drain, soakaway or rainwater | Check downpipes and drains, ask about springs |
| Wet patch on the road side of the meter | Communication pipe or main | Report it to South West Water |
| Wet patch with a smell near a chamber | Foul drain fault | Drainage contractor, not a water leak |
Who pays for what
In Cornwall, South West Water is responsible for the water main in the road, the communication pipe and the meter up to the boundary stop valve. The supply pipe from the boundary to your house belongs to you, and so does the repair. A wet patch in the front garden between the meter and the house is therefore usually your pipe. South West Water offers a leak allowance on a first supply pipe leak, subject to its conditions, which can take some of the sting out of the bill for water that soaked into the lawn. Our guide to the South West Water leak allowance explains how to apply and what they ask for. Get the leak repaired promptly and keep the evidence, because the allowance normally depends on both.
Buildings insurance is a separate question. Many policies cover the damage a supply pipe leak causes, and some include underground pipe cover or trace and access cover, which contributes to the cost of locating the leak and reinstating the ground or drive that had to be opened. The failed pipe itself is not normally covered. Read your schedule, and if you are a landlord, remember that keeping the water supply installations in repair is your obligation under section 11 of the Landlord and Tenant Act 1985.
How a buried leak is located without digging
The wet patch is a clue to the area, not the answer. Water can travel along the outside of a pipe or through a gravel bed and surface some distance from the fault, so digging where the grass is greenest often finds sound pipe and a lot of mud. A specialist survey finds the point first.
- Tracing the pipe. The route from the meter to the house is traced and marked so the search follows the pipe rather than the lawn.
- Acoustic listening. A ground microphone amplifies the sound of water escaping under pressure. On a long run, correlation equipment compares the sound at two points and calculates where between them the leak sits.
- Tracer gas. Where the pipe is plastic or the leak is too small to hear, a safe hydrogen and nitrogen mix is put into the pipe and detected where it surfaces through the ground.
- Cross checking. The repair point is marked only when two methods agree, so the one hole that is dug is the right one.
The result is a marked spot on the ground and a report your plumber or groundworker uses to open a short trench and replace the failed section. On an old iron or lead pipe they may recommend replacing the run in blue MDPE rather than patching, which is often the better long-term answer. Our underground water leak detection service covers gardens, drives, farm supplies and shared pipes across the county, and we provide leak detection across Cornwall from the Tamar to Land’s End.
What to do this week
Do the meter test tonight and again tomorrow. Photograph the patch, the meter readings and the date. If the meter confirms a leak on your side, tell South West Water so the allowance clock starts, and arrange detection before anyone digs. Do not leave it for the winter. A small leak softens the ground under paths and walls, undermines a drive, and on sloping Cornish plots can wash fines out from under a retaining wall. The bill runs up quietly the whole time.
Frequently asked questions
Why is one patch of grass greener than the rest of the lawn?
Constant moisture from a leaking pipe below feeds the grass above it all day, every day, so it grows thicker, greener and faster than grass that relies on rain. The same patch usually stays wet through dry spells. Do the water meter test to confirm whether the water is coming from your supply pipe.
How do I know if the wet patch is a spring rather than a leak?
A spring is cold, often on a slope, wetter in winter and after rain, and usually predates the current owner. A supply pipe leak is steady in all weathers and makes the meter move with the internal stopcock closed. If the meter does not move at all with everything off, a spring or a drain is more likely.
Who is responsible for a leak on the supply pipe under my garden?
You are, from the boundary stop valve into the property. South West Water looks after the main, the communication pipe and the meter up to the boundary. South West Water offers a leak allowance on a first supply pipe leak, subject to its conditions, so contact them once the leak is confirmed.
Can a garden leak be found without digging up the lawn?
Yes. The pipe route is traced, then acoustic listening, correlation and tracer gas are used to pinpoint the escape from the surface. The repair point is marked once two methods agree, so the groundworker digs one short trench in the right place rather than following the wet patch.
Will home insurance pay for a leaking supply pipe in the garden?
Many policies cover the resulting damage, and some include underground pipe or trace and access cover for locating the leak and reinstating the ground. The pipe repair itself is not normally covered. Check your own schedule, and keep the meter readings, photographs and the detection report to support a claim.
Find the leak before you dig
If the meter keeps turning with the stopcock closed and the lawn will not dry, we can pinpoint the escape on your supply pipe from the surface. You get a marked repair point for your groundworker and an insurance-ready report.
