the flow of diluate in a diluate manifold 232 the electrodialysis membrane stack arrangement 210 however primarily differs from the electrodialysis membrane stack arrangement 10 by the placement or positioning of a single calcium exclusionary cationic selective membrane 220 f as the cathode cell boundary all other cationic selective membranes within the electrodialysis membrane stack are non exclusionary cationic membranes more particularly and especially in processing of streams or waters containing high concentrations of soluble calcium it has been found that the cationic selective membrane at the cathode is beneficially a special membrane material that allows for the transport of monovalent cations such as sodium but limits the transport of divalent cations such as calcium or magnesium or other multivalent metals that form precipitates with the anions present in the electrolyte solution furthermore the selective membrane at the anode desirably should allow transport of all cationic species those skilled in the art and guided by the teachings herein provided will understand and appreciate that practice of the invention can desirably prevent avoid minimize or overcome at least some of the above discussed problems associated with transport of soluble calcium into the electrolyte solution for example practice of the invention can desirably prevent avoid minimize or overcome problems associated with transport of soluble calcium into the electrolyte solution such as leading to increased resistance to ion flow by fouling the electrode cell specifically at the cathode such as by the formation of precipitated calcium salts such as calcium hydroxide or calcium sulfate and the resulting reduction in the effective amperage of the electrodialysis stack at a specific voltage moreover compounds containing other divalent cations with similar chemistry to calcium including specifically.