Method 557 is a direct-inject, ion chromatography, negative-ion electrospray ionization, tandem mass spectrometry (IC-ESI-MS/MS) method for the determination of haloacetic acids in finished drinking water. Bromate and dalapon (2,2-dichloropropionic acid) may be measured concurrently with the haloacetic acids. Real time, chromatographic separation of common anions in drinking water (matrix elimination) is a key feature of this method. Acceptable method performance has been demonstrated for matrix ion concentrations of 320 mg/L chloride, 250 mg/L sulfate, 150 mg/L bicarbonate and 20 mg/L nitrate. Method 557 requires the use of MS/MS in Multiple Reaction Monitoring (MRM) mode to enhance selectivity. Precision and accuracy data have been generated for the detection of nine haloacetic acids, bromate, and dalapon in reagent water, synthetic sample matrix, and finished drinking water from both ground water and surface water sources. The single laboratory Lowest Concentration Minimum Reporting Level (LCMRL) has also been determined in reagent water.