The influence of magnetic fields on the physico–chemical properties of water and aqueous solutions is well known. We have previously shown that weak combined magnetic fields with a 60 µT static component and a 100 nT (at 12.6 Hz) variable component are able to activate neutrophils, both directly and indirectly, through water pre-incubated in these fields. The ability to influence the activity of neutrophils was retained in serial dilutions of water, but only when a mechanical effect (shaking) was applied at each dilution step. Here, we confirm that combined magnetic fields are required for the formation of the stimulatory activity of water on ROS production by neutrophils. For the first time, we determined the threshold values of a constant magnetic field (at least 350–550 nT) necessary to maintain this activity in a series of successive dilutions. Additionally, the biophysical properties of various dilutions appeared to be not identical. This confirms that the number of technological steps (successive dilutions with physical influence) is a key factor that determines the activity of highly diluted samples.