I've conducted a lot of geophysical surveys to identify drill sites for water wells. Once a local dowser was also given a shot and I was amazed at the amount of correllation between our picks. Hundreds of acres surveyed and several of my top targets were also identified by the dowser. Keep in mind we were not working over regional aquafers, but searching for intersections between water-bearing fractures in bedrock - specific spots. Hocus-Pocus? Perhaps...
Nowadays, I work for the state permitting private water wells and other stuff and know all the drillers in the area. Almost all of them like to dowse a property before committing to a spot. Some are more serious about it than others and it doesn't work all the time, but most consider it "another tool".
So I wouldn't necessarily can a driller just because he carries a forked stick or a pair of wires or a nut on a string, but just like hiring any contractor you'll want to check out more than one. Then decide whether to go with the stream or try a well.
