Let's talk about the science for a moment instead of dowsing, and look at the data from historical experiments. The evidence tends to support the radiation hypothesis.
I'm sure we're all familiar with Baron von Pohl's
map-dowsed surveys of Vilsbiburg and other German towns in the late 1920s showing a correlation between underground water and the beds of cancer victims (if you're not familiar, have a quick look under 'modern research' here
Von Pohl's work was developed by other researchers, such as Pierre Cody
in the 1930s, who experimented with gold leaf electroscopes and showed that radiation rose vertically from underground water veins in a tight band, which caused ionisation of the air directly above. Experiments with lead sheets blocked this radiation and discoloured the lead sheet after a period of time. He concluded that the ionisation was most likely caused by alpha particles. Cody also demonstrated that the noxious energy could be detected in the upper floors of a building with no apparent deviation or change in width (more recently, Swiss nuclear physicist Angelo Communetti
repeated this experiment and found that the column of radiation deviated 15 degrees eastwards from the vertical in tall buildings).
In 1955, Dr. Josef Wüst
used a Geiger counter to detect very small increases in gamma radiation under ‘cancer beds’ in the town of Pleutersbach in Germany.
In the 1970s Jakob Stängle
had continued this line of research by developing a ‘scintillation counter’ that was much more sensitive to gamma radiation and other charged particles. Essentially it optically amplifies the minute flashes of light that the charged particles produce in a Geiger counter, making it many times more sensitive. It was a bulky device, and as it is wheeled along it registers variations in the background radiation; it was particularly effective at detecting water lines and oil deposits.
Stängle repeated von Pohl’s survey of Vilsbiburg, completely vindicating von Pohl’s results. “The principal objection against the existence of pathogenic stimulation zones, namely the inability to objectify them, is no longer valid.”