Perturbations on the earth’s magnetic field may coincide with the existence of groundwater. Theoretical calculations are made showing how and to what extent this effect may exist. The suggestion is also made that water dowsers may get a dowsing reaction as a result of entering a change in magnetic gradient. Tests were conducted to determine the statistical significance of dowsing reactions obtained by separate individuals dowsing in a common test area. Approximately 150 people participated in the experiment over a period of one year. Chi-square tests showed considerable statistical significance. Virtually all people tested experienced dowsing reactions though most of them had never dowsed before. There is some evidence of correlation between magnetic gradient changes and dowsing reactions.
Chadwick, Duane G. and Jensen, Larry, "The Detection of Magnetic Fields Caused by Groundwater" (1971). Reports. Paper 568.