The paper has its focus on water's key functions behind ecosystem dynamics and the water–related balancing involved in a catchment–based ecosystem approach. A conceptual framework is being developed to address fundamental trade–offs between humans and ecosystems. This is done by paying attention to society's unavoidable landscape modifications and their unavoidable ecological effects mediated by water processes. Because the coevolution of societal and environmental processes indicates resonance rather than a cause–effect relationship, humanity will have to learn to live with change while securing ecosystem resilience. In view of the partial incompatibility of the social imperative of the millennium goals and its environmental sustainability goal, human activities and ecosystems have to be orchestrated for compatibility. To this end a catchment–based approach has to be taken by integrating water, land use and ecosystems. It is being suggested that ecosystem protection has to be thought of in two scales: site–specific biotic landscape components to be protected for their social value, and a catchment–based ecosystem approach to secure sustainable supply of crucial ecosystem goods and services on which social and economic development depends.