Thirteen years after the beginning of the democratization process in South Africa, many radical socio-political and institutional transformations have taken place in the country. Unlike during the Apartheid era, natural resource management and governance, particularly in the water sector, is nowadays based on concepts and criteria such as decentralization, economic efficiency, environmental sustainability and social equity. These criteria, which represent the pillars of the South African National Water Act (NWA-1998), are universally recognized as the fundaments of sustainable development and are widely employed in the definition of the environmental policies of the industrialized countries. To accompany this socio- political revolution, a process of institutional building is taking place in the South African water sector. New organizations, namely the Catchment Management Agencies (CMAs) and the Water Users Associations (WUAs) in charge of local governance of water are being established in the country. These new organizations urgently need tools, methods, processes that can help them in their difficult task of implementing locally the NWA by promoting the participation of local stakeholders in the process of water management and allocation. In particular, there is a need to gain a better understanding of collective decision mechanisms. In the South African context, participatory approaches - involving local stakeholders, decision-makers and researchers- have been implemented to accompany the water allocation process at catchment scale: the Kat River catchment was used as a pilot study to develop a role-playing game (KatAware -based on multi-agent simulations) accompanying the negotiation between water users on the allocation rules of irrigation water. However, the lessons of this experience are not easily transferable to other sites or situations. The objectives of our work are therefore to assess the impact of the context on the outcome of a collective decision: b