"Water has always been considered either a public good (in most cases) or a private one when it is appropriated to generate economic value, for instance in bottled water. Only at very local scales, water users communities have created institutions that manage water as a common pool resource as has been extensively documented by the work of Elinor Ostrom. The basic problem with water is that it is, by nature, a multi-scale resource: water is used for many purposes and managed at many different levels (local, regional, national, international). It is also multidimensional, its management requires dealing with social, economic, hydrological and climatic data, which is difficult to collect and usually not shared and coordinated among different institutions and scales.