The Short Version
This claim is not supported by scientific evidence. The U.S. Geological Survey, systematic reviews, and controlled studies consistently find that dowsing performs no better than chance. The rod's movement is explained by the ideomotor effect (unconscious muscle movements), and apparent successes are attributed to the high prevalence of groundwater in many regions and dowsers' unconscious reading of surface cues—not detection by the rod itself. No properly controlled scientific test has validated dowsing as a method for locating underground water or minerals.