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Samples of untreated source water and finished drinking water were obtained from 42 water utilities which treated their water with oxidants–disinfectants that included chlorine dioxide (ClO2), gaseous chlorine, hypochlorite solutions, and chloramines. Chlorite ion was only detected in water from utilities that used ClO2. Finished water from utilities that used ClO2 or hypochlorite solutions contained comparable concentrations of chlorate ion (ClO3−) in the range 21–660 μg/L. Analysis of the hypochlorite solutions indicated ClO3− contamination was a greater problem in the solutions purchased in concentrations >10 percent available chlorine. Low levels of ClO3− (10–81 μg/L) were also detected in approximately one third of the untreated source samples.

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The development of the U.S. Environmental Protection Agency (EPA) Method 317.0 is initiated to provide a sufficiently sensitive and fundamental technique for the compliance monitoring of trace levels of bromate in drinking water. After a comparative evaluation of Method 317.0 and elimination of a chlorite interference, this method is tested by a collaborative study in order to determine the precision and bias of the method and evaluate its potential role as a future compliance-monitoring method for inorganic disinfection by-products (DBPs) and trace bromate. This technique provides a practical method for future compliance monitoring for all of the inorganic oxyhalide DBPs including trace concentrations of bromate.