Carboxylic acids are of interest to water utilities because they are readily biodegradable. In ozonated waters they have been found to comprise the largest identifiable fraction of assimilable organic carbon, and they are a potentially significant source of food for bacteria growing on filter media and in water distribution systems. Existing analytical methods available for monitoring carboxylic acids and subject to one or more of the following limitations: inadequate sensitivity; inability to determine certain analytes of interest or to determine all analytes of interest using a single injection; interferences associated with major anions (chloride, sulfate, and bicarbonate); and, variable or incomplete recovery of certain analytes, especially when analyzing relatively hard waters. To overcome these limitations, an improved ion chromatography (IC) method, suitable for determining a broad range of carboxylic acids in drinking water supplies high in hardness and dissolved solids, was developed. The method includes sample pretreatment to remove chloride, sulfate, and bicarbonate without significant loss of the analytes of interest, large-volume injection, analyte separation using a high-capacity column and an optimized gradient, and detection using suppressed conductivity. The estimated detection limits of the method are 1 to 3 ug/L for glycolate, propionate, formate, pyruvate, oxalate, and ketomalonate, and 10 to 20 ug/L for acetate and glyoxalate in waters containing a small amount of fluoride. Includes 12 references, tables, figures.