There is no real controversy to it, it's hogwash. Its walking around with a stick and pointing at a random point on property. It doesn't matter which part of your property you dig, there is or there isn't groundwater to be had, 100m here or there makes no difference. There usually is though, so seemingly the water witch is almost always validated. Nobody digs at all the other places the witch doesn't point to in order to check if maybe those have water at the same depth too.