A system of deionizing water having a plurality of vertical ion-exchange columns connected in sequence by pipes comprising a housing enclosing one of a cation, an anion, or a mixed-bed exchange resin and at least two regeneration columns supplying strong base to the anion-exchange column and strong acid to the cation-exchange column whereby the columns are mounted on a frame structure, characterized in that the resin in each ion-exchange column is sandwiched between two plates, the upper plate is moveable arranged such that it moves towards the lower plate as the resin is depleted, thereby compressing the resin in the housing to prevent canal formation within the resin.