I was asked the following question recently.
Can a thermal camera be used to find a leak under a concrete floor?
This is an excellent question, and one that I am often asked. The short answer to this is yes, but it does need to be a sufficient leak to cause a temperature variation on the surface. If the leak is very small, or the pipe is too deep this might prevent a temperature variation on the surface, also if the leak is oriented so as to run away very fast into the subfloor, it may not be detectable. In addition to this, it is possible to get a false indication of a leak. This happens if a pipe is placed closer to the surface than others or if several pipes are located close together. So false positives and false negatives are possible. This is one of those things that is worth trying, but it is not 100% certain that every leak will be detectable, and it is not 100% certain that everything detected will be a leak. Verification of the anomalies detected is usually required.