As someone who used 4 different geologists/diviners at different points of time, I believe no method is perfect. And I have to admit my worst results are from the most scientific method.
My first experience was with a diviner who used L rods. I can vouch the L rods moved based on some force beyond the person’s muscles; however all I managed to get at the identified points was some wetness, nothing more.
Then I decided to get scientific and engaged a proper geologist who used electrodes for the resistivity method. Drilling at the points he identified was 100% failure!
The third was a person who used an egg, copper plate and coconut. I myself sat on the coconut in the plate to be rotated at high speed with the person controlling the rotation from hundreds of feet away! The points did not yield water, though I would give the benefit of doubt that the drilling happened many months after the points were identified.
The latest experience was with a local person who used a coconut that rotated in his hand. The points led to reasonable success, though we had been very specific with auspicious timing for the drilling etc. 
All in all, there are real forces in action in divining/dowsing. Whether the forces actually indicate water or some other phenomenon is subject to debate. I have been reading more about dowsing lately and some theories even suggest that the movements are based on suggestions from spirits in the area, though the scientific explanation is involuntary muscle movements. Clearly there is more than what meets the eye! 