AbstractWe present a novel multichannel membrane flow‐stream capacitive deionization (MC‐MCDI) concept with two flow streams to control the environment around the electrodes and a middle channel for water desalination. The introduction of side channels to our new cell design allows operation in a highly saline environment, while the feed water stream in the middle channel (conventional CDI channel) is separated from the electrodes with anion‐ and cation‐exchange membranes. At a high salinity gradient between side (1000 mm) and middle (5 mm) channels, MC‐MCDI exhibited an unprecedented salt‐adsorption capacity (SAC) of 56 mg g⁻¹ in the middle channel with charge efficiency close to unity and low energy consumption. This excellent performance corresponds to a fourfold increase in desalination performance compared to the state‐of‐the‐art in a conventional CDI cell. The enhancement originates from the enhanced specific capacitance in high‐molar saline media in agreement with the Gouy–Chapman–Stern theory and from a double‐ion desorption/adsorption process of MC‐MCDI through voltage operation from −1.2 to +1.2 V.