Diagnosis of changes of deionized water characteristics (conductivity, pH and redox potential) due to different ways of degasation and 170 MHz frequency electromagnetic field irradiation has been carried out. Studies have shown one-sided changes in the properties of water at various ways of its degasation and high-frequency electromagnetic field irradiation. Increase of conductivity and pH and decrease of redox potential has been found to take place regardless of the impact on deionized water. Degasation by evacuation and purging with an inert gas leads practically to the same result. The change of water characteristics is to the maximum extent the result of high-frequency electromagnetic field impact. The change of oxygen concentration in water under different ways of exposure is considered with the help of auxiliary equation derived in the course of work. The decrease in the concentration of oxygen dissolved in water is shown to be the result of evacuation, bubbling with nitrogen and high-frequency electromagnetic field irradiation. Kinetic curves of the change of electroconductivity, Ph and redox potential change have been obtained. They indicate that the degree of properties change depends on the method and duration of the exposure.