I used this once when I was hunting for a bottle of beer in a bucket of ice. It didn't work, so I used my hand. I threw away the twig.

Water! You mean there's water underground! What a bizzare, freaking concept!

This is more art than science, and one that I've never been convinced actually works. Like anything else, if you make enough guesses, eventually you'll be right.

Pretty amazing: you walk over land, and the stick moves when you pass over groundwater. Well guess what folks, there's groundwater everywhere: it's all a question of how deep you have to drill to get to it, and its quality when you get there.