In the 20th century, water management focused on the local scale of interest. In the 21st century we will be facing changes in quantity and quality of our water cycle. Triggering forces behind these new challenges are industrialisation, population growth and the delayed awareness that we are to expect a global change. The magnitude and distribution of global changes are not exactly predictable, because we live in an always changing environment, are faced with severe and interfering processes, which all are not yet sufficiently understood. Therefore, to shoulder this task, hydrology should embrace more integrative and interdisciplinary approaches than already existing and has to achieve more flexibility in assessments and decisions. To better approach this challenge, catchments related solutions are more important than local solutions, to satisfy the water demand of agriculture, ecosystems, industry and the private sector. And we should keep in mind that the environment has a "sustainable memory" and our knowledge about attenuation capacities and resilience of the environment is still low.