A method of operating a reactor for removing impurities by electrochemical means from liquids, such as aqueous solutions. The liquid is passed through series of plateshaped reaction electrodes electrically insulated against each other with a liquid speed above a minimum to prevent dissociation into constituent gases, but sufficient to ensure interaction with an electrical current passing between the plateshaped electrodes. The latter has corrugated forms and/or their surfaces provided with embossed relief patterns to enhance the electrochemical effect between the electrodes. The conductivity of the treated liquid, the organic contents of the liquid and the flow of the liquid is measured and the length of the flow path for the liquid in the reactor is established in dependence on the measured parameters. Ultrasonic vibrations are generated in the flow path for stimulating a reaction process.