If a water pipe is not under pressure or the noise from the leak cannot easily be heard then Tracer gas can be a very useful technique to locate water leaks in: Customer Supply Pipes, Underfloor Heating Systems, Boilers, Central Heating Systems, Mains Distribution Networks.
When a pressurised water pipe leaks the water flows out which causes the pipe and surrounding material (mud, concrete tarmac) to vibrate. This sound, or vibration, is transmitted along the pipe (structure borne water leak noise) and through the surrounding material (ground borne water leak noise).
When Tracer Gas and Acoustic Detection draws a blank Thermal Imaging can be used to trace the water leak. A thermal imaging camera cannot see moisture in walls, but it can detect subtle temperature differences and patterns that reveal the existence of water.
We would be pleased to discuss your requirements with you.