For the improvement of the performance of technical processes, faults and abnormal system operation must be detected and identified. For that purpose different approaches for fault detection have been developed and, here, a model-based approach is used. A diagnosis strategy based on fuzzy residual analysis is presented in this paper. The proposed approach uses the analytical redundancy to detect and isolate faults on sensors. After a presentation of its principle, the method is applied to an urban water supply network. Thanks to the use of fuzzy concept, the suggested diagnosis procedure enables to take into account all the available data and knowledge. Moreover, its efficiency has been proved by using experimental data. Therefore, a supervision software has been developed on the basis of this fuzzy-based fault isolation method. (C) 2006 Elsevier Ltd. All rights reserved.