In order to investigate the origin of the radon from 20 ground water samples, a relationship between radon and radium levels was investigated as in Fig. 4. The correlation coefficient was then estimated to be 0.12.There is a weak linear correlation between 222Rn and 226Ra in these samples. This suggests that the majority of 222Rn found in water samples did not originate from 226Ra compounds soluble in water. The biggest concentration of 222Rn may have originated from gas exhalation by the soil adjacent to the well due to a difference in physical–geographic characteristics of underground sources of water. The geographical characteristics of water regions with different concentrations of 238 U in rock, soil and water, or the temperature, salinity and turbidity of water may play a key role in accelerating the rate of increase of 222Rn concentrations in these 20 ground water samples