Capillary membrane sampling-flow injection analyzer (CMS-FIA) analyses of drinking water samples for quantity measurements of total trihalomethane and haloacetic acid contaminants therein are provided. With the necessity to chlorinate drinking water to remove harmful bacteria and other potential toxins, trihalomethane and haloacetic acid byproducts are generated that may harm humans after consumption as well. A reliable manner of measuring such drinking water supplies for such trihalomethane and/or haloacetic acids at locations far from the source and closer to dispensers is highly desirable. The CMS-FIA analysis method of the invention has been found to be nearly as reliable as source measuring methods for the same purpose, but with the versatility to measure for such trihalomethane and haloacetic acid contaminants anywhere along the drinking water supply line.