For simple water distribution systems, mean residence times may be measuredby tracer studies, or estimated using hydraulic models. A tracer analysis performed in a complex water distribution system is a delicate operation, and one which depends on a very precise knowledge of the system (instantaneous configurations, variation of water consumption). To obtain sufficiently accurate residence times, and tobe able to identify the number of paths the water takes and how much each contributes to the sampling point, reliable and rapid analysis techniques which can be automated are necessary. The objective of this study was to improve tracer techniques and residence time analysis using tracer results subjected to signal processing. A method using spectral analysis has been developed based on numerical and laboratory tests and then applied to an actual water distribution system. The method is based on the recognition of injected frequencies at a given sampling point. The application of the method to an actual water distribution system provided good results and allowed the authors to determine the potential and limitations of this promising technique. Includes 22 references, tables, figures.