I remain open minded as to whether it works or not, but I would have to point out that the James Randi Foundation still have their million dollars as no one has been able to prove the existence of ESP and Dowsing is one of the disciplines they will test for if asked.
Well ...it's not really surprising as the parameters they set were pretty ridiculous and very limiting:
" On April 1, 2007, it was ruled that only persons with an established, nationally recognized media profile and the backing of a reputable academic were allowed to apply for the challenge, in order to avoid wasting JREF resources on frivolous claimants.
[105] "
Secondly:
" In 2015, the James Randi paranormal challenge was officially terminated due to Randi's retirement from, and thus lack of direct involvement with, the foundation. "
He was actually more interested in the paranormal .. claims of mediums that they could communicate with the dead and people who claimed they could read minds and communicate via ESP and the likes of people like Uri Geller and his spoon bending trick.
The on;ly dowsing incidents he was involved with was the 'Bomb dowsing' device - Sniffex - which comes under my definition of a charlatan based fraud ... The other one was someone who claimed they could identify playing cards sealed in an envelope with a pendulum ...
Dowsing for these sort of things is outside of the dowsing I've experienced of dowsers finding naturaly underground water sources and my own and others experience of locating lines of force within the earth's crust and I would accept they are of dubious veracity.