The development of a decision or policy support system is a very time consuming and expensive process. Reusing an existing system provides therefore major benefits. This paper describes the process followed when applying the existing MedAction Policy Support System, developed for Northern Mediterranean regions, to the Oum Zessar watershed in south east Tunisia. The paper presents the differences and similarities of the problems and processes in the different regions and describes how they relate to the adaptation of the existing model and the place the system could take in the decision-making process. Furthermore, it discusses the likelihood of its actual uptake in the Tunisian context based on six criteria discussed in a participatory approach with potential users of the system.