Abstract : In this paper, direct water quality modelling and the associated unsteady sensitivity equations, are solved in Water Distribution Systems (WDS). A new solution algorithm is proposed, based on a time splitting method to separate and solve efficiently each phenomenon such as advection and chemical reaction. This numerical approach allows a simultaneous solution of both the direct problem and the sensitivity equations. Special attention is given to the treatment of advection, which is handled with a Total Variation Diminishing (TVD) scheme. \\ The general model presented in this study permits a global sensitivity analysis of the system and its efficiency is illustrated on two pipe networks. The importance of the sensitivity analysis is shown as part of a fitting process on a real network.