A novel electrodialysis (ED) pilot plant unit coupled with a membrane stack containing 11 cation-exchange and 10 anion-exchange membranes is used for the removal of nitrates and hardness from simulated aqueous mixtures containing salts that are usually encountered in brackish water. The removal of high nitrates and water hardness is performed in 150 min of ED under three constant applied voltages at room temperature. The limiting current density is obtained for sodium nitrate and calcium chloride mixtures in dilute solution. In order to check the efficacy of the ED method, parameters like the applied potential are varied at constant flow rates. The efficiency of the ED method depends on the applied potential. Possible applications of ED are discussed for the removal of contaminants below the minimum contaminant level of drinking water. The ED method used here is satisfactory to produce good quality drinking water from a simulated mixture by removing the unwanted ions. (c) 2006 Wiley Periodicals, Inc.