I should know better than to post on this thread, but I just can't help myself..
A couple years ago we built a new house, when the excavator guy was done putting in the driveway (first thing we did), I asked him about a test hole for a well. He asked me if I had a couple of old coathangers to witch it with.. me being me, I just smiled and said I'd see what I could find. As it happened, the wife was there on her horse, and she rode across the field to a neighbour's and "borrowed" a couple of coat hangers.
Jeff straightened them out, then bent a six inch 90 degree "leg" in each one. Asked me where I thought the best spot for a well would be. We've got a swampy area on the back of the property, so I started him out in that direction. 5 minutes of walking with the rods dangling slightly down from the "handles" and a couple of ground scuffs later, he told us the only ground water he had found was on almost the highest point of the property, and nowhere near the swamp.
Skeptical me said "I'm finding it hard to believe that.." Jeff grinned, passed me the rods, and said" You give it a try and tell me what you think" He showed me how to hold them, loosely horizontal with a slight nose down angle, and walk along. He said, " When they try to cross each other, you're in the right place..."
Feeling a little foolish, I started walking around. I covered the same ground he did with a few variations, purposely avoiding the spots he'd marked. Nothing, not even a twitch. Feeling pretty confident now, I walked across the "line" of spots. The look on my face was worth a million bucks, never mind absolute proof. Two pieces of supposedly inanimate metal that had been holding sweaters until an hour ago were telling me I was crossing some magical line in the earth... Honest to God.. it's an uncanny feeling, I'll tell you that much!
Watching from a comfy saddle, the wife's eyes took on a much more interested light. She hops down, says to me in a tone that brooked no argument, "Hold the horse, I've got to try this one myself..." She passes me the reins, grabs the coathangers, and off she goes. Found the exact same spot Jeff and I had. Her eyes were mirrors of mine, disbelief is putting it mildly.
Sixteen feet of digging later in hard clay and gravel, we watched a side wall of the hole first dampen at about the 10 foot level, then start to cave in as water pressure acted on the wall of the hole. We've had lots of water since then, once the seams fully opened up. The excavator bucket smeared them shut on the first pass. We might have found water most anywhere on the property, but I DO know we found it there. Maybe by coincidence, maybe not, it's in a direct line between the two neighbours' wells. An aquifer maybe?
His explanation of the phenomonon is that moving water creates a magnetic field that attracts the rods. It's why he wanted steel rods. He said he had no luck with wood, but had used coat hangers to find buried pipes over the years. He did say he had to flush water through the pipe to make it work in some cases.
Another neighbour used him to dig a well a few years back. They had dug holes all over he** and creation in the low spots, a lot of dry holes. He found a spot the others hadn't tried, on the very top of a hill on the property. I'm talking a decent size field, maybe 25 acres. The owner just shrugged and said "What's one more hole?" There was water there all right, enough to water 25 horses on a daily basis.
Do I understand it? He** no ! Do I believe in it? You bet I do...
Chilly
The earth is also the center and the sun goes around us, after all that is what the majority said. There are no such things as atoms,.,.,., show me one, with the naked eye 
