Abstract: A method of tracing sewage effluent is described in which samples of fluid flows are subjected to high performance liquid chromatography with respective elution systems capable of eluting different selected compounds therefrom, and the concentration of each compound in the sample is determined spectroscopically. The method is used to determine sewage flow paths in natural water bodies, such as rivers, to check for contamination by sewage, to determine possible sewage sources, the detection of uric acid, for example, being indicative of a human source; and to monitor the effluent from sewage treatment plants.