In the three Forest Models territories Jujuy (BMJ, Argentina), Chiquitano (BMCh, Bolivia) and Araucarias de Alto Malleco (BMAAM, Chile), water security problems are subject to exacerbation by climate change. Issues pertaining to water quality, availability or both, need to be tackled collectively by the actors of a same watershed, given their interdependencies when managing natural resources. In this context, where the EcoAdapt research-action project is operating, our objective is to promote a common understanding of the issues at stake on water security and the corresponding socio-ecological dynamics that might either worsen the current situation or lead to solutions. To this end, we proceed in two steps, co-building successively in each of the three watershed sites two main products : a conceptual model that provides a synthetic representation of how the socio-ecosystem functions around the water security problem; and a historical profile of the last five decades that characterizes successive development phases marked by various occurrences or disturbances (new policy measures, cooperation interventions, market fluctuations, climatic event...). Based on the Resilience approach and nurtured by a learning-bysharing process amongst the actors of each territory, this analytical method produces threshold cascades allowing the participants to visualize the possible impacts of new climate event o policy reform. In the three territories, equity issues emerge, confronting: upstream versus downstream actors in Argentina when reacting to water scarcity risk and trying to secure access to water for irrigation; communal smallholders versus private largeholders in Bolivia when adjusting their cattle raising practices and pasture expansion to new policy measures; water rights owners versus water users in Chile when the legal conditions enhance speculative water management. Addressing theses equity issues in water management decision-making appears a necessary way to prevent conflicts and non-cooperative responses to climate change threats. (Résumé d'auteur)