As a youth (1980's) I worked for a guy who was called in by Anglian Water to find leaks when they couldn't and he travelled all over their vast area.
It was all cash in hand and off the books, as he was a dowser!
He used to tell them how deep the pipe was, its diameter and construction, which way the water was flowing and the type of leak. Basically everything they needed to know and without having to break the surface.
I remember him telling the AW manager who used to call him in, that a particular broken clay sewerage pipe would pollute a pond 60 feet higher and 400 yards away and being roundly laughed at. AW decided not to apply any urgency to the fix and nearly 3 weeks later the pollution started! (He could 'feel' the type of soil and rocks and knew that capillary action (although he didn't know the name) would have a significant effect.)
ICON : ironic, as there is no scientific reason for dowsing to work - except that it does in the hands of one of the very few people who still 'knows' how. (Not me - I could follow an underground structure, but not know the difference between a dry mole drain and a large mains water pipe!)