Abstract: An apparatus for electrochemical treatment of contaminated water or wastewater comprises a container or tank having an inlet and an outlet and a feed pump for the water to be treated, connected to the inlet for supplying the water through the inlet to the container or tank. Parallel pairs of electrode plates are situated in vertical position in the container or tank and form parallel vertical passages therebetween for the water to be treated. In the pairs of electrode plate at least one electrode plate comprises holes connected to a feed pump for an auxiliary medium. Said pairs of electrode plates are positioned between the inlet and outlet in the container or tank such that in at least part of the flow route between the inlet and outlet the water passes upwards in the vertical passages. The feed pump for the water to be treated and/or the feed pump for the auxiliary medium is a pulsating feed pump.