People have been finding water with forked sticks ever since Moses brought forth water by smiting a rock with a rod. Chinese texts tell of water witching 4000 years ago. Agricola's famous 15th-century mining text describes it. For millenia people have believed in something with no rational basis. Dowsing takes many forms.
Some dowsers openly claim paranormal powers.
The best of them say they neither know nor care how it works, but they're sure they can find water. The worst wrap their divining rods in bogus science. Marine Corps engineers at Camp Le Jeune brought a dowser in and studied his technique during the Viet Nam war. They wanted to find enemy tunnels and hidden arms. Engineers reporting back to the Pentagon picked up that theme.