Drinking water treated with chlorine or chlorine dioxide contains a mixture of different chlorine species. Their identification, especially at low concentrations, is still problematic because of the number of compounds produced, especially when mixtures of chlorine and chlorine dioxide are used. This research investigated the determination of trace chlorate concentrations in drinking water in the presence of chlorite ion by spectrophotometry. Spectrophotometric methods for the determination of chlorate ion are uncommon because these methods are affected by the presence of chlorite ions in drinking water. The aim of this research was to determine small amounts of chlorate impurities in the presence of chlorite ions by spectrophotometry based on the production of a coloured haloquinone by reaction of chlorate with benzidine in a hydrochloric acid medium. The results showed that the proposed spectrophotometric method is rapid, accurate and simple. The method was also compared with conventional ion chromatography.