Ground water is a subsystem of the hydrogeological circle, which is very complex and among all subsystems the hardest to reach. Therefore, great efforts to characterize groundwater flow in unsaturated as well as saturated zone are being made. The characterization of groundwater flow in the saturated zone was tackled by means of water tracing in order to model the transport of pollutants through an aquifer. The major stress was put on the characterization of ground water flow through the unsaturated zone of an aquifer. Our work was divided into two segments: intergranular aquifers and karst aquifers. In order to study intergranular aquifers we set an experimental polygon, while karst aquifers were studied through indirect analyses, e. g. analyses of larger karst springs. The results of our investigations contributed to the understanding of the reactions of an aquifer to recharge and infiltration, mostly from the point of view of short-term reaction. Apart from the characterization of ground water flow, ground water protection plays an important role in our research. Within the frame of that research we studied interactions between a source of pollution (e. g. waste disposal site, motorway) and the ground water system. The results of these investigations contributed exceedingly to the knowledge about the flow tracks of pollutants through an aquifer as well as their interaction with the surrounding material, which enables detailed risk analysis and environmental impact assessment. We also take part in international geochemical investigations (Project IGCP 360 - Global geochemical bases), which will result in new principles and directives for the methodology of modern geochemical investigation at regional and detailed scale, which are intend to yield knowledge about current geochemical state on one side and pre-civilisation, natural state on the other.