A water treatment apparatus comprising a stack of circular electrodes with a central through hole, the electrodes are supplied with electricity so as to form anodes and cathodes in alternating intercalation. The anodes and cathodes so arranged to lie in such close-spaced parallel face to face relationship as to form a capacitive deionization cell. Water to be treated is passed from the outside of the stack, radially inward through between the electrodes into the central through hole and then axially out of the stack.