A system for treatment of water and/or wastewater is being developed. Pulsed high voltage applied to electrodes immersed in a water stream creates high potential gradients in the water volume between the electrodes. These gradients have a bactericidal action. In addition, ozone can be generated throughout the water volume by introducing air in fine bubbles from a sparger. The applied gradients create ozone and chemically active radicals within the air bubbles. The system has several advantages including: (1) No persistent chemicals are added to the water, (2) High gradients can be employed by themselves or combined with ozone generation, (3) Ozone is generated within the volume of the water being treated, and (4) Chemically-active radicals are produced within the water volume, together with ozone.