The effect of high-frequency electromagnetic field on the surface tension of deionized water, characterized by a higher degree of purification in comparison with distilled water has been investigated. It is shown that 6–10% increase of surface tension depending on electromagnetic field frequency and the time of exposure takes place. The studied frequency range is 100 MHz to 200 MHz in 10 MHz steps. Exposure time varied from 30 minutes to 4 hours. Changes in surface tension are to the most extent expressed at frequencies 130 and 170 MHz and the exposure time of one hour. The efficiency of field impact was found not to depend on the volume of the cell where water irradiation was carried out. Surface tension does not change for a long time after impact termination. Water irradiation also leads to the raise of its boiling temperature, evaporation heat and evaporation rate. Since all specified properties are determined by the power of intermolecular interaction within the liquid it is suggested that the observed effects are caused by the increase in the proportion of water bound into clusters and by hydrogen bonds network hardening.