How do you tell a drainage leak apart from a mains pipe leak?

Full transcript

George and Dave in conversation. Every word of the episode, exactly as recorded.

George

Welcome to the ADI Leak Detection podcast. I'm here with Dave from ADI Leak Detection, the country's leading name in leak detection, who's here to answer your questions and provide expert leak detection advice. Today's question is one that genuinely puzzles a lot of homeowners: if you've got water escaping somewhere on your land, how do you actually tell whether it's a drainage problem or a mains supply problem? Dave, over to you.

Dave

It's a great question because the two get confused all the time. The single quickest check a homeowner can do themselves is look at their water meter. If the meter's spinning when every tap, appliance and toilet is off, water is escaping from the pressurised supply side. A drainage leak won't touch the meter at all, because drainage pipes carry no mains pressure.

George

So a still meter rules out a mains leak completely?

Dave

It rules out a pressurised supply leak, yes. But it doesn't rule out a drainage problem. Drains fail silently from a meter's point of view. You'd notice it as damp patches in the garden, soft ground, unexplained subsidence, or sometimes a persistent smell. Those are the signs that send us down the drainage investigation route rather than the supply route.

George

Right, so once ADI's engineers arrive on site, what's the actual process for working out which system is the culprit?

Dave

ADI's engineers start with a pressure test on the supply pipework. We isolate the internal plumbing from the external supply pipe and apply a test pressure. If the supply holds pressure, the problem isn't on the mains side. If it drops, we know water is escaping from the pressurised system and acoustic listening equipment then pinpoints exactly where along that pipe the leak is occurring.

George

And acoustic detection, that's the kit that listens through the ground?

Dave

Exactly. Acoustic leak detection works because a pressurised pipe leaking underground generates a very specific sound signature. Our engineers use sensitive ground microphones and listening rods to pick up that sound through tarmac, concrete, soil, whatever's above the pipe. Acoustic equipment pinpoints the leak location far more precisely than digging blind, which saves a huge amount of disruption to the property.

George

Does acoustic detection work the same way on drainage pipes?

Dave

No, and this is where the distinction really matters. Acoustic leak detection relies on pressure to generate that sound. A gravity drain has no pressure in normal operation, so there's no acoustic signal to follow. For drainage investigations we switch methods entirely. Tracer gas locates drainage leaks by introducing a harmless gas mixture into the drain run, which escapes at the point of failure and is detected at ground level with a gas detector. CCTV survey is another route, sending a camera through the drain to show a crack or a joint failure directly on screen.

George

So the method changes completely depending on which system you're investigating. Is it ever genuinely unclear which one is to blame when you arrive?

Dave

Occasionally, yes. You can have both failing at the same time, particularly on older properties. And some symptoms overlap. Wet ground in the garden could be either. In those cases the pressure test is the first decision point because it gives us a definitive yes or no on the supply side. Once the supply pipe is cleared, any remaining damp has to be investigated as a drainage issue. We don't assume it's one or the other and start digging.

George

That makes complete sense. Is there anything a homeowner should be doing while they wait for an engineer to attend?

Dave

Check that meter and make a note of the reading, then check it again after thirty minutes with nothing running. If it's moved, photograph it. Note where any damp patches or soft ground are on the property and roughly when you first noticed them. That information genuinely helps the engineer focus the investigation rather than starting from scratch. Don't start lifting paving or digging yourself though, because disturbing the ground can mask the acoustic signal we rely on.

George

That's really useful, practical advice. Dave, thanks for explaining that so clearly. If you're dealing with unexplained wet ground or you suspect a leak on your land, ADI Leak Detection is one of the UK's most trusted specialist teams in the field. Get in touch and their engineers will identify whether it's your supply or your drainage that needs attention.

How this episode was made. This episode was produced using AI-generated voices and script, based on real leak detection questions and the working knowledge of ADI Leak Detection engineers.