The T-He age dating method uses the ratio of the concentration of radioactive tritium (3H) derived from atmospheric nuclear bomb testing and its decay product Helium (3He) in the groundwater to determine a groundwater age, i.e. the time passed since the water had its last contact with the atmosphere. At the Free University of Berlin, hydraulic and hydrochemical processes accompanying bank-filtration are currently examined at two very different locations: In metropolitan Berlin and the rural Oderbruch polder region. The city of Berlin enhances bank-filtration through well galleries located adjacent to the surface water system. The spatial and temporal development of the bank filtrate is studied in cooperation with the Berlin Waterworks and the Berlin Centre of Competence for Water at several exemplary piezometer transects. The system generally behaves highly transient due to continuously changing pumping regimes. At the gallery Lake Wannsee, the well filter screens are pumping water from 3 different glacial sand layers separated by aquitards. The well water is a mixture of very old deeper groundwater, medium old water from the middle layer and very young bank-filtered water. The Oderbruch is located north-east of Berlin aside the river Oder. Intensive melioration activities in the past 250 years converted the former swamp into a fertile, agricultural region and lead to the permanent infiltration of river water into the shallow, confined aquifer. Compared to Berlin, the infiltration is a long-term, very stable process. The groundwater is getting older with increasing distance and travel-time from the river. The concentration of “stable” tritium (sum of 3H and tritiogenic 3He) increase from the river inland reflecting the decrease of 3He in the atmosphere from the early 60’s onwards. Peak concentrations are encountered in 2.1 km river distance whereas further inland (3.4 km river distance) old water which infiltrated prior to the nuclear bombing peak is encountered. In addition, the groundwater has a high radiogenic 4Heterr concentration which also indicates that the groundwater is more than a few decades old. Even further inland, in the central polder areas, the groundwater is unconfined and continuously recharged to some extend by percolating water infiltrating through shrinkage fissures in the overlying dried alluvial loam. The water is a mixture of young seepage water and very old bank filtrate, the resulting “mixed” T-He age is getting younger again. The T-He method was successfully applied to support estimated groundwater ages derived from tracer analysis (e.g. 2H, 18O, EDTA, Gd) at both locations. In the Oderbruch, the T-He ages were used to calibrate a flow model. The method also proved to be a very good indicator for the identification of mixing processes.