Capacitive deionization (CDI) is a non-membrane and chemical-free technique for water purification, used-water recycling, and seawater desalination. Ionic contaminants in the waters are retained by a static electric field built within the critical component of CDI, which is known as flow through capacitor (FTC). Apparently, parameters enhancing the field strength of FTC and electrode efficiency are the keys to the performance of CDI. The FTC of the present invention is formed by a plurality of monopolar and a plurality of bipolar electrodes, and a plural number of perforated holes are disposed on the FTC electrodes in a pattern that allows certain water flow rate and residence time to yield the highest efficiency of electrode utilization.