This is a large volume (2 to 4 mL), two-dimensional (2-D) ion chromatographic (IC) method using suppressed conductivity detection for the determination of perchlorate in raw and finished drinking waters. Because this method utilizes two dissimilar IC columns it does not require second column confirmation. Detection and quantitation in the second dimension are accomplished by suppressed conductivity detection. Precision and accuracy data have been generated for perchlorate using this 2-D IC method in reagent water, finished groundwater, finished surface water and a Laboratory Fortified Synthetic Sample Matrix (LFSSM). The single laboratory Lowest Concentration Minimum Reporting Level (LCMRL) has also been determined in reagent water.