The isotopic signature and time information can be used to trace water provenance, recharge processes and geochemical reactions, to derive transit times, and to investigate flow paths and coupled ecohydrological processes. These are crucial factors in order to estimate the vulnerability and the recovery-time of water bodies impacted by pollution, to define drinking water protection areas, to plan the sustainable use of water resources and to protect ecohydrological systems, and to quantify quality problems due to climate or land use change. This session wants to bring together experience of applied resource management and advanced research dealing with the application of isotopes and water ages by different techniques (traditional and newly developed isotopes, tracer techniques, modeling, etc.) with the goal of managing the quantity/quality of surface- and groundwater in the frame of global change at various spatial scales.