The practical quantitation limit (PCIL) for arsenic (As) is currently orders of magnitude higher than its nonenforceable, health-based standard in California. Analytical limitations caused by chloride (CO interference can be overcome using high-resolution, inductively coupled plasma mass spectrometry (ICP/MS), which has a method detection limit for As of 29 ng/L in the presence of 35.5 mg/L Cl. Increasing Cl concentration (0-355 mg/L) resulted in a nonlinear increase in the As signal. Therefore, standard addition was used to test four water samples with unknown As and Cl concentrations. Because standard addition is not suitable for routine analyses, further investigation of matrix effects and interferences is needed to optimize the application of high-resolution ICP/MS forwater qualitytesting. Nonetheless, broader adoption of this and other methods for trace As analysis could result in lowering of the KIL for As in the future, with consequent downward pressure on reporting levels.