Electrochemical technologies for the treatment of industrial and municipal wastewaters, potable water, and groundwater, are presented, focusing on the main water constituents: inorganics, organics, micropollutants, and microorganisms. Removal of inorganic compounds by electrodialysis, electrocoagulation, and capacitive deionization as well as removal of organics and micropollutants by electrosorption, advanced oxidation processes, and anodic oxidation with boron-doped diamond electrodes are reviewed. Electricity can be generated by degradation of organic compounds in microbial fuel cells and dehalogenation by cathodic reduction minimizes toxic substances in water. The disinfection of different types of water is also presented and it is shown that electrochemical methods offer versatile approaches to contribute to an sustainable future water management.