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. These methods require low technical effort. At Aquifer Storage and Recovery and ponded infiltration the recharged amounts are technically controlled. The infiltration water has to be pumped and often pretreated. At bank filtration this is dispensable, the approach, of using existing surface water bodies is even more consequent. Exemplarily, at a test site at Lake Tegel, Berlin, Germany, the hydraulic processes 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. A new inverse modelling concept has been developed and applied to a 3D short term local and transient hydraulic model. It comprises spatially distributed pilot points and overparameterisation constrained by regularisation and calibration to head differences. Significance of the results is demonstrated by cross validation. With this approach the spatial distribution of an aquitard have been identified with high precision. The highly transient and heterogeneous flow conditions are specified and a new viewpoint on the geologic formation of Lake Tegel is obtained. The good fit of modelled and observed breakthrough curves of 18O, chloride and temperature by just using transferred parameters obtained with the previous hydraulic methods, show the very good model performance and predictive capabilities. The intrusion of atmospheric oxygen into the unsaturated zone is identified to be the principal redox determining factor during infiltration. Previously inconsistent and also local geochemical conditions are identified to be determined by interaction of infiltration processes with the spatial extent of the aquitard. A theory for chemical clogging of abstraction wells is developed, identifying the strong vertical redox zoning as principal factor of influence.

Access to microbiologically and chemically safe water is limited not only in developing countries, but also in transition Countries and even in remote areas of some developed countries. For these cases, point-of-use (POU) technologies can be promising alternatives to centralized treatment concepts. Membrane-based treatment systems have gained importance for drinking water treatment in the developed countries and can be considered as the dominant technology for new applications at present. Due to the high retention of pathogens and the possibility of downscaling (modular construction) membrane technology seems to be attractive also for application as POU system in developing and transition countries. However, no scientific publications on such systems are available and application is limited. Therefore we conducted an extensive literature and state-of-the art review to evaluate relevance, current use and the research and development needs of membrane-based POU systems in developing and transition countries. POU technologies are widely being used to produce safe and high quality drinking water in rural areas of industrialized countries, where access to centralized supply is not available, or for additional treatment of tap water. However, the cost level of POU systems applied in industrialized countries is in general not acceptable in other cases. Therefore simple low cost systems were developed and applied in developing and transition countries. In a range of case studies, described in literature, these systems show themselves as an appropriate short term solution, but often fail to provide improved access to necessary amounts of safe water. Economical growth of developing and transition countries leads to increasing public concern, affordability and requires long term sustainable solutions of the drinking water problem. Membrane-based POU/POE systems are especially attractive for application in developing and transition countries while they can provide high removal of bacteria, protozoa and viruses, have modular design and can be operated with a range of different energy sources, including mechanical and hydrodynamic energy. But, for their application in developing and transition areas, the cost level is in general not acceptable. Furthermore, the source water quality is often very low and can differ regionally as well as seasonally, and the POU/POE systems should be able to treat this kind of waters. Another critical factor in transition and especially in developing countries is the maintenance and control. Not only the level of education of the local population may be insufficient, but also structural financial means for maintenance and control may be lacking.