This is a difficult one, because so far there is no scientific or rational explanation for it, only speculation and testimonies. It’s about dowsing and about what the French call “geo-biology”, that is: the study of energies and vibrations peculiar to a place. And of the impact and influence those energies have on the physical behavior of plants and animals, and on the psyche of humans.
Magnetic currents, often called telluric currents, travel throughout the earth’s surface. The underground is crisscrossed with water veins, sometimes flowing, sometimes still. There are also a lot of faults in the earth’s crust, emitting radioactivity among others. The electromagnetic disturbances caused by solar activity, the influence of the moon and cosmic rays react with the telluric activities to form what could be called a “vibratory tissue”. This tissue has nodes, where the different “energies” interpenetrate to form powerful turbulences, “hot spots” so to speak, where the negative ionization of the air is stronger. It is a proven fact that high concentrations of negative ions in the air give us a boost, because they suppress serotonin levels in the blood, in much the same way that natural sunlight suppresses melatonin levels. We could say that negative ions are essential for high energy and positive mood.
These hot spots were seen as meeting places between man and the organizing forces of the cosmos, where man could connect with them. This is the origin of the word religion: religare, to (re)connect. Most of these energies can’t be experienced directly by the senses. So a dowsing rod or pendulum is used to detect them, and to translate them into a kinetic movement.
Water veins under the church of Avioth, France, as seen by a dowser
Water veins under a dolmen