Conceptual obstacles to holistic water management are: (1) the compartmentalized approach taken by most water professionals, representing typical differences in their sectoral focus; (2) scientifically-based paradigms which are incompatible with water's vast complexity, roles and functions, including the quantity/quality bias hydrology/ecology bias linked to geoscience and bioscience, respectively.
There is also the difference between "visible" and "invisible" water. Engineers focus on visible water (blue water), which they can control and regulate. Invisible water (green water) in the soil and air has tended to vanish from focus. For example, dryland productivity has been discussed as a soil issue rather than specifically the presence or absence of water in the root zone. This typifies the conventional dichotomy between land and water, which in Agenda 21 were treated more or less as independent phenomena. Water rarely appears as significant in land productivity in temperate areas. For instance, since European settlement of Australia and the transformation of virgin woodlands into croplands, as much as 10 percent of the former evapotranspiration/green water flow had been transformed into blue water flow in the rivers. Similar changes in the blue/green water partitioning of precipitation have been reported from the Hungarian Plain.