My grandfather always said that 2 lines on your have to intersect/connect to do ,as you can see mine don't
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He would just find a branch in the shape of a "Y" ,he then would hold the "V" with his palms up ,and start walking around until he would start to feel "pull" and would stay walking in the same direction if the "pull" stopped he would turn around and go another direction until he would find the strongest spot (I have seen his hands scrapped up from a branch being pulled out of his hands ) . He could aslo tell you how deep the water was and was always 6".
There was 1 time I went with him , one of his relatives called cause their well dried up ,and the driller was there and already drilled 2 holes , so they told the drillers ro stop, and called my grandfather, we went over he walked to a tree cut a branch , started walking around after about 10-15 minutes or so , he told the drillers drill here 75feet down, they argued with him for a little that there can't be water there ,finally they drilled where he told them to, 75 feet they hit water they couldn't believe it.
I'm not sure why he always said that metal rods didn't work.
I will say he didn't have a very open mind
Hope this gives you a little info