Streamflow is known to be fed from time and space variant contributions from saturated and unsaturated zones. Eventually, the state of the hydrological system is expressed through the volume of water stored in a catchment as snow, soil moisture, groundwater and surface water. To date, we still lack understanding of how spatial and temporal variability of streamflow age components are related to flow processes and wetness conditions in catchments. Further, it is poorly understood how physiographic catchment properties control the characteristics of catchment storage, transit time and transit time distribution. Here, we intend to tackle these open questions by combining research on dynamic catchment storage based on a multi-method approach and the application of tritium and stable water isotopes (2H, 18O) to calculate time variant transit times and their distributions. By bringing together these two fundamental descriptors of catchment functioning, we target to better understand how catchments collect, store and release water. Eventually this will lead to a better classification scheme for catchments, and to more advanced and sophisticated water resources management strategies under external forcings, such as climate and land use change.