Dowsing, Divining water, metals & other things Options

I am naive in this field but I have seen some diviners dowsing to a breath-taking accuracy. For example, there are persons who would dowse on a map with a pendulum and the pendulum would vibrate at the exact spot-point below which water or the treasure is there and they will tell at what exact depth the desired thing can be found.

I was once part of a woodland maintenance team, and once we had to fell a windblown tree which had lodged itself into a neighbouring tree.
This presented a hazard to people in the vicinity, and so had to be felled.
There was another problem, in that the area where it would land, had a large water pipe below the surface of the field, and to ascertain the exact location of the pipe, we tried dowsing with two bent rods which crossed at a certain point when we walked across the area.
After digging down at this point, we found the pipe, and took measures to avoid breaking it.
Unfortunately, all my subsequent attempts to find lost objects, and leaky pipes have failed, but I am still convinced that it works, just that I'm not very good at it.
If anyone can give any hints or tips as to how this technique can be developed, I would be greatly interested.
Steve.

P.S. Does this count as spell begging?