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Casein/starch composites are shown to act as potential candidates for binders of symmetric carbonaceous electrodes used in the capacitive deionization (CDI) of water. Casein and potato-starch biopolymers are cheap and environmentally friendly and may be implemented throughout a green process to obtain a carbonaceous CDI electrode using sole water as a solvent. It was found that among the different starch/casein mass ratios considered in this study (0 : 1, 1 : 1, 2 : 1, 1 : 2, 1 : 4 and 1 : 0), the ratio 1 : 2 resulted in an optimal CDI performance corresponding to 12.7 mg g−1, 50% and 1.01 W h g−1 for salt adsorption capacity, charge efficiency, and specific energy consumption, respectively. The outstanding performance observed is attributed to the formation of a binder with a hydrophilic mesoporous network carrying inherent positive and negative charges throughout the internal surface area, inducing both anion and cation-exchange membrane characteristics in the binder layer. For the optimal binder composition, the latter network possesses a dominant pore diameter of 4.65 nm, while the dominant pore diameter is less than 3.00 nm for the other samples, eventually enhancing ion species mass transfer through the polymer matrix. [ABSTRACT FROM AUTHOR]