1) SOUND – Listening sticks, ground microphones, correlating loggers, leak noise correlators.
PROS: easy to use, reliable results, technology very well understood having been in use for many decades.
CONS: small leaks, or plastic pipe, or low pressure don’t produce enough noise to be picked up from some distance away at a nearby valve or hydrant, or to travel effectively through the ground.
Noise generating features in the water pipe such as partially closed valves, and Tees, many times will show up as a leak.
2) TRACER GAS
PROS: Only looks for the presence of gas on the ground, independent of ambient noise.
Very effective at identifying small leaks, or leaks in plastic pipe.
Helium and mix of Nitrogen+Hydrogen are safe to both humans and are inert (no chemical interaction with gaskets, pipe material or the water).
CONS: need to inject Helium or Nitrogen+Hydrogen upstream into the line.
May require service to be interrupted.
Practical for pipe diameters up to approx. 10-12 inches
3) THERMAL IMAGING
PROS: Very easy to use.
CONS: There must be enough temperature difference between the ground and the leaking pipe in order for the system to detect the leak area.