Several kinds of managed aquifer recharge techniques provide very good purification of surface water since more than 100 years. In order to maintain a reliable supply of clean water, they are becoming increasingly popular all over the world. Especially bank filtration methods require low technical effort. Exemplarily, at a test site at Lake Tegel, Berlin, Germany, the hydraulic processes of infiltration are modelled. By means of 3D long term regional and transient hydraulic modelling it was detected that the existing approaches for determining the leakance induce large errors in the water balance and describe the infiltration zone insufficiently. The leakance could be identified to be triggered by the groundwater table, causing air exchange and intrusion of atmospheric oxygen, which reduces clogging by altered redox conditions by at least one order of magnitude. This causes that changes of the groundwater table are mitigated much more than previously assumed. Taking these findings into account, a transient water balance is determined and bank filtration ratios are quantified.