Until not long ago, I was working in the drilling and infrastructure business. Some people I was working with used metal rods as a "quick and dirty" method of detecting underground wiring, before bringing in the full power Ditch Witch.
What they did was to take two metal rods (brass or copper, not sure) that are hanged on some pin so they can freely spin horizontally. The person moved it around the surface until the rods aligned with the (supposed) wiring. Surprisingly, this worked.
This is not some magical detection of water with wooden sticks, but rather light weight metals (possibly) interacting with an electromagnetic field generated by underground wires carrying electric current.
Some more info: one of the men also used this to "detect" concrete sewage pipes. I don't see why this would work. He also knew there were underground wires around, just not the exact location.
Can underground wires cause horizontal rotation of metal rods, held above the ground?