How does a pressure wave find a water leak under a floor?

Full transcript

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

George

Welcome back. Today we're talking about something that sounds almost like magic, using sound to find a hidden water leak under a solid floor. I'm here with Dave from ADI Leak Detection, the UK's leading leak detection specialists, who's here to answer your questions and provide expert leak detection advice. Dave, the question I want to dig into is: how does a pressure wave actually help you locate a leaking pipe?

Dave

Right, so when a pipe develops a hole or a crack, water escapes under mains pressure. That escaping water doesn't just quietly drip, it creates a vibration at the point of the leak, and that vibration travels outward through the pipe wall and into whatever material surrounds it.

George

So the pipe itself is carrying the signal? Like a kind of ringing?

Dave

Exactly. The pipe becomes a conductor. That pressure wave moves along the pipe in both directions from the leak. What we're doing with acoustic detection is listening for that wave and working out where it's coming from.

George

And how do you actually pick it up? Because if it's under a concrete floor, I can't imagine it's loud.

Dave

It's not loud at all to the human ear, which is why we use specialist equipment, ground microphones and acoustic sensors that we place directly on the floor surface or on exposed pipe fittings. Those sensors are sensitive enough to detect the frequency signature of a water escape even through thick concrete.

George

So the engineer is moving a sensor around the floor listening for... what exactly?

Dave

The signal gets stronger the closer you are to the leak. So one technique is simply scanning along the pipe route and noting where the signal peaks. But the more precise method is acoustic correlation, which is where it gets really accurate.

George

Tell me about correlation, I've heard the term but I don't really know what it means in practice.

Dave

Acoustic correlation places two sensors on the pipe, one on each side of the section you're investigating. Both sensors pick up the pressure wave from the leak, but the wave reaches them at slightly different times because one sensor is closer to the leak than the other. The correlator measures that time difference and, knowing the pipe's material and diameter, calculates exactly how far the leak is from each sensor.

George

That's genuinely clever. So you're triangulating using the delay rather than the volume.

Dave

That's a good way to put it. The time-of-arrival difference is the key measurement. Acoustic correlation can locate a leak to within a few centimetres on a straight run of pipe, which means we can mark the floor and the excavation is kept as small as possible.

George

Does the floor type make a big difference? Like, does a solid concrete floor behave differently to tiles or a timber floor?

Dave

It does. Dense materials like concrete carry the acoustic signal well, so the pressure wave stays relatively clean. Timber floors, on the other hand, absorb and scatter the signal more, which can make the reading noisier. Our engineers adjust the equipment sensitivity and filter settings to account for that.

George

And what about pipe material? Does copper behave differently to plastic?

Dave

Very much so. Copper and iron transmit the pressure wave efficiently, the signal travels fast and stays strong. Plastic pipes, particularly modern polyethylene supply pipes, dampen the wave more quickly. ADI's engineers account for pipe material when setting the correlation parameters, because the speed of sound through the pipe changes depending on what it's made from. Get that wrong and your location calculation is off.

George

So there's real skill in interpreting the data, not just plugging in equipment and reading a number.

Dave

Absolutely. The equipment gives you data; the engineer interprets it. Ambient noise, traffic, boilers, other appliances, can all produce frequencies that interfere with the leak signal. Experienced engineers recognise what a genuine leak signature looks like versus background interference, and that distinction matters on a busy residential street.

George

Dave, that's been a really clear explanation of something I'd assumed was quite mysterious. Thanks for breaking it down.

Dave

Happy to. The short version is: the leak makes noise, the pressure wave carries that noise along the pipe, and our equipment finds where it's loudest and when it arrives. The rest is physics.

George

Perfect place to leave it. If you've got a water meter spinning with everything switched off, or damp patches appearing with no obvious source, ADI Leak Detection are specialists with a national reputation for finding hidden water leaks accurately and without unnecessary damage. Thanks for listening.

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. More about how the podcast is made.