There are people that claim they can tell you where water is via a dowsing rod. Water finding. Water witching. Water Divination. I’m gonna spoil it for you: it’s hogwash.
Dowsing has been a pseudoscience employed since the 1500s, and it was just as useless then as it is now. Traditionally the way it works is that you take a forked twig, hold it in front of you, and it’ll make small movements towards what you’re trying to find.
The small movements are said to be magnetic ion something something by divinators. Those small movements are known as the Ideomotor phenomenon. It’s where a mental image or a thought bring on a reflexive muscular action outside of conscious knowledge. It’s the same effect that you’ll see with other “precognition-lite” techniques like Ouija boards, automatic writing, and facilitated communication. (Sorry if I’ve dunked on your preferred pseudoscience, happy for you to tell me how I’m wrong.)
It’s been tested again and again and show that it’s a whole bunch of baloney. While the 1990 study by Hans-Dieter Betz concludes that it works, but statistical analysis by J. T. Enright in 1995 finds that out of 500 dowsers even the best of the best were about only 0.4% better than random chance which could be easily attributed to statistical fluctuation. That’s the most POSITIVE study I can find on it; there’s countless others that call out dowsing as completely fake. Algeria 1943, New Zealand 1948, Britain 1959, the British Ministry of Defense did one in 1971 - the list goes on and every single one of them show this as a complete farce.
Even today, water dowsing is employed by ten out of the twelve water companies in the UK. Dowsing is considered “tried-and-tested” methods of finding water by these companies, if Twitter is to be believed. Really.
The ADE 651 and GT200 are modern versions of the dowsing rod being sold in military applications as late as 2011 and have been found just as effective as previous dowsing rods. Read: They’re as good as random chance because that’s all it is. They say they can track drugs, bombs, ivory, and who knows what else. What’s even more amazing is they’re purported to be powered by the user’s static electricity and they have programmable cards that you have to pay extra for because of.. electrostatic magnetic ion … It’s a huge fake and by 2010 companies of both swindled people out of millions and millions of dollars. This includes the governments of the USA, United Kingdom, Iraq, Lebanon, Thailand, and Mexico.
The creators of these devices are currently being litigated so thoroughly that they’ll need a dowsing rod to find themselves out of the mess they’re in.
Thing is - if you have other sensory cues, you use your mind, and with the observer expectancy cognitive bias - dowsing really works! At least, it works about as well as me going out into that same field and rolling a D20.