Fast changes in spring water quality in karst areas are a major concern for production of drinking water and require detailed knowledge of the complex interaction between karst aquifer, transport behavior of microorganisms and water treatment We have conducted artificial and natural particle transport experiments at a karst spring with bacteria, bacteriophages, microspheres, and pathogens Transport of the investigated microorganisms, turbid matter and chemical pullutants as well as increase in discharge are strongly related to precipitation and the heterogeneity of the aquifer The indicator bacteria E cob revealed a significant correlation to verotoxin-producing E cob and Cryptosporidium spp We conclude that artificial particle tracers can help identify "hot spots" for microbial recharge and that system parameters in spring water such as turbidity, UV-extinction and increase in discharge can be key parameters for efficient raw water management.