The need to guarantee sustainable water resource management is increasingly apparent at both national and European level. The complexity of situations that need to be regulated is becoming a central issue to the policies concerned due to the multiplicity of interdependencies and causal links that have to be taken into account. In this paper, we propose a model to analyze how public action deals with this complexity. From applying this model to the implementation of instruments for sustainable water resource management in France and the United Kingdom, it appears that while the objectives appear to be convergent, the policies follow quite different learning trajectories, leading them to construct and objectify water as a "common heritage" in different ways.