A flow-through electrolytic cell for removing heavy metals from waste water has a cell housing (1) with an inlet (7) and an outlet (8) for solution to be treated at opposite ends. Foam metal cathodes (3) are arranged in the cell housing transverse to the housing and extending over its entire width, with coated titanium mesh anodes (4) interleaved between the cathodes. The anodes (4) are contained in diaphragm-forming boxes (2) of microporous ion-permeable material. Each box (2) forms an anode compartment and has means (5, 6) for circulating anolyte therethrough. The boxes (2) extend partly across and are offset alternately from opposite sides of the cell housing (1) to provide a serpentine path for liquid to be treated (catholyte) flowing from the inlet (7) to the outlet (8) through the cathodes (3). The anolyte circulation includes a siphon (20) for controlling the anolyte head to prevent unwanted mixing of the anolyte and catholyte. The cell is useful for the treatment of rinse waters from chloride-containing baths, organic-containing plating baths, rinse waters containing multi-oxidation-state metallic ions, and spent baths from the electroless plating of nickel.