At present, there is a growing interest in the study of possible applications of plasma discharge water treatment technology in various industrial fields. The equipment considered in this work is based on the combined effect on water of plasma discharge and cavitation in flowing mode. The optimal design of the installation was determined. Many authors note the possibility of regulating the growth and development of plants of various crops as one of the promising applications of this technology. Previously, physicochemical processes occurring in water during plasma discharge treatment have been investigated, and the formation of reactive oxygen species (ROS), including hydrogen peroxide, in treated water has been noted. ROSs are actively involved in regulation of plant growth and development. Adjustment of the power of electric pulses supplied to the reactor of the plant allows controlling the generation of hydrogen peroxide. The aim of the work was to determine the most effective mode of water treatment to regulate the growth of lettuce variety “Tuscan” of the genus Lettuce of the Aster family (Lactuca sativa L.). When watering lettuce with water treated in the most effective mode, the dry weight of lettuce increased more than 2 times, and the ascorbic acid content increased by 40%.