The performances of four commercial anion-exchange membranes in the extraction of nitrate ions from water were compared in dialysis against a concentrated sodium chloride solution. The characteristic time derived from a simplified transport model for ion dialysis appears to be a convenient quantitative criterion for a selection of the best membrane for the removal of an undesirable ion. For the nitrate removal from sulfate-containing water to make it drinkable, the Neosepta ACS anion-exchange membrane appears to be the best choice due to the fast and selective removal of nitrate obtained.