Regarding the treatment of (waste)water, electrochemical processes have various advantages over other methods. They are robust, easy to operate and flexible in case of fluctuating wastewater load. In addition, a relatively broad spectrum of organic and inorganic impurities can be removed. This contribution provides an overview of electrochemical reactors for water, process water and wastewater treatment, which are already in technical-scale operation or subject of research. Some essential basics of electrochemical processes for the treatment of water are presented and examples for applications are given. This is followed by a description of the reactors.