Mains Water Leak Detection

A mains water leak usually announces itself on paper before you ever see water. The bill arrives two or three times higher than normal, or the meter keeps creeping round with every tap in the house turned off, or South West Water writes to say their readings suggest a leak on your supply pipe. The pipe itself sits buried under the drive, the lawn or the path, so the leak can run for months without showing on the surface.

After more than 30 years finding leaks across Cornwall and Devon, we know exactly how that conversation goes. The good news is that a mains leak is one of the most findable leaks there is. The pipe is under constant pressure, it follows a single run from the boundary to the house, and our equipment is built for precisely this job. We mark the leak position before anyone lifts a slab, with no call-out fee, a fixed price agreed up front, and No Find, No Fee on residential work (subject to terms).

🚨 Signs of a leak on your mains supply pipe

Mains leaks have their own signature, different from a leak inside the house. The ones we confirm most often started with one of these:

• The meter keeps moving with everything off. The classic giveaway. If the dials or digits advance overnight with no water used, water is escaping somewhere between the meter and your taps.
• A sudden, unexplained jump in your water bill. Nothing about your routine has changed, but the metered usage has. Our guide to a high water bill with no visible leak walks through what to rule out first.
• A letter from South West Water. Their meter readings or network monitoring suggest water is being lost on your side of the meter.
• Low water pressure at taps that used to run strongly, especially the kitchen cold tap fed straight off the main.
• A wet, soft or sunken patch on the lawn, drive or path along the line the pipe takes to the house, or a stretch of grass that stays lush and green in dry weather.
• A hissing sound near the internal stopcock or outside stop valve when the house is quiet.

One or two of these together is a strong signal. The meter test below confirms it in an evening, without spending a penny.

📏 Whose pipe is it? Supply pipe responsibility explained

This is the question every mains leak job starts with, because it decides who pays. Ofwat, CCW (the Consumer Council for Water) and South West Water all set it out the same way:

So when people talk about a mains water leak at home, they almost always mean the supply pipe: the stretch from the meter or boundary to the building. That is the section this page covers. If your problem is a buried leak somewhere else on the property, a garden irrigation run or an external pipe that is not the incoming main, our underground water leak detection service covers buried pipework of every kind.

Shared supply pipes are common in older Cornish terraces and converted farm buildings, where one pipe feeds several properties. Responsibility is then usually shared between the owners it serves, which is one more reason to have the leak located precisely before anyone starts negotiating over a repair.

📬 Had a letter from South West Water? Here’s the position

A leak letter feels like a bill waiting to happen, but it is also the start of a process that can work in your favour. South West Water, like all water companies in England and Wales, runs a leakage code of practice. Under it, a metered customer can normally apply for a leak allowance from South West Water, which writes off water lost through a hidden supply pipe leak, usually for the first leak at the property and on condition the leak is repaired promptly. The company may also offer help towards a first-time supply pipe repair, subject to its conditions.

The sequence matters. The allowance follows the repair, and the repair follows finding the leak. A professional detection survey with a written report gives you the evidence that there was a genuine hidden leak, where it was, and when it was fixed, which is exactly what the allowance application needs. If you have just received a letter and are not sure what order to do things in, our step-by-step guide to what to do when South West Water says you have a leak takes you through it.

There is a bigger picture too. Ofwat and CCW report that around three billion litres of water a day are still lost to leakage from pipes in England and Wales. Finding and fixing your leak quickly keeps your money on your side of the meter and takes one small leak out of that total.

🔍 How we trace mains leaks without digging

The old way to find a supply pipe leak was trial holes: dig along the pipe run until you hit wet ground. On a Cornish drive over granite, that gets expensive fast. We do it the other way round. The equipment finds the leak first, and the only ground that gets opened is the small area directly over it.

Because the supply pipe is pressurised, every leak on it leaves traces that the right kit can read from the surface.

🧪 The meter test: confirm it yourself tonight

Before you book anyone, you can confirm a suspected mains leak with your own water meter. Take a reading last thing at night, use no water overnight, and read it again first thing. If the numbers have moved, water is escaping somewhere on your side of the meter. If you are not sure which dials matter, our guide on how to read your water meter explains each type.

To narrow it further, turn the internal stopcock off and watch the meter. Still moving? The leak sits on the supply pipe, between the meter and the house, rather than in the indoor plumbing. Our article on a water leak between the meter and the house covers what that means and what happens next. Bring the readings with you when you call; they tell us roughly how big the leak is before we arrive.

🛡️ Insurance, trace and access and the supply pipe

Most UK buildings insurance policies include trace and access cover. In plain terms it usually pays for professionally locating the leak and making good the damage caused by reaching it, though it does not always cover the repair of the pipe itself and policy limits vary, so check your own wording. The Association of British Insurers’ guidance on escape of water claims says the same: locating and accessing is the insurable event, the faulty pipe is often not. Our plain-English guide to what trace and access cover is goes through it in detail.

Every mains detection survey we carry out can come with an insurer-ready report: photographs, the marked leak position, the methods used and the readings taken. If you would rather have the detection and the documentation handled in one visit, our trace and access service does both.

📋 What to expect on the day

A mains leak survey is straightforward and tidy. A few things speed it up:

• Know where your internal stopcock and your outside stop valve or meter are. The meter is usually in a small chamber at the boundary, under a plastic or metal lid.
• Have a recent water bill to hand, plus any letter from South West Water.
• Note your overnight meter readings if you have done the test above.
• Tell us what the drive and paths are made of and whether the pipe route has ever been moved, as older properties often have the pipe in an unexpected place.

On the day we confirm the leak, trace the pipe, pinpoint the position and mark it clearly, then talk you through the repair options and the paperwork for South West Water or your insurer. The price is the one agreed before we arrived, and if we don’t find a residential leak, you don’t pay (subject to terms).