I do not know how it works, and I do not think it works as expressed. I know of the other hand people using a wooden branch, they find water, more often than by chance. Some can tell you the future using cards, they have right to a extend more than by chance. I do not think it is the cards, it is people who can read you, and see what you likely will be up to. I think the same is here, they can read the topography, and point out the water, maybe not knowing the way they work themselves.