Continuous Electrodeionization (CEDI) is the process of removing ionized or ionizable substances from water using ion exchange membranes, electrically active media (typically ion exchange resin), and a DC electric potential. 

Feed Water is feed through a series of alternating dilute and concentrate compartments with electrode compartments at either end. The feed water (RO permeate) to be deionized is fed through the dilute feed compartments with a fraction of the flow being diverted to the concentrate and electrode feed (internal) compartments. The ion exchange resin accepts the ions in the feed water just as in conventional ion exchange, subject to the usual mass transfer and thermodynamic equilibrium.
EDI is truly the only chemical-free method of producing high purity deionized water.