In our rapidly urbanising world, population densities no longer allow for unlimited access to safe water. The growing competition for water, often associated with a competition for access to land, tend to be exacerbated in peri-urban areas : the cities fringe supports the urban expansion processes, very diversified modes of land occupation and, in many developing countries, most of the poverty. Thus, urban expansion in these areas are often associated with the growth of shanty towns with inadequate sanitation arrangements, and enhanced pollution runoff. This lead to various tensions and conflicts that needs to be better managed. The intention of this paper is to present the management issues of the peri-urban upstream catchment of Sao Paulo (Brazil) and the main lines of an action research-project aiming to facilitate negotiation over land and water management in this context. The paper starts by presenting the context of land and water management in the Metropolitan Region of Sao Paulo (Brasil). The challenges due to the implementation of new legislation over water and municipal management are then discussed. Finally, the main lines of a new project, based on the combined use of multi-agent modelling and role game playing are presented.