Emerging contaminants (EC) are a major environmental issue because of their constant release into the environment. Based on a case study, a nontarget screening was performed on the drinking water treatment chain at Hardwald to investigate possible unknown EC's and to examine the performance of the di erent cleaning steps. This thesis describes the establishment of a fast, automated workflow in R to obtain a (complete) nontarget list from liquid chromatography-high resolution mass spectrometry data. It was shown that these lists could be used to investigate the nontarget pattern changes across the drinking water treatment chain at Hardwald by assessment of the amount, the intensity distribution and mass and retention time of each nontarget in the nontarget pool. Across the treatment chain, a general decrease in amount and intensity of the nontargets could be observed. The most important step was observed to be the riverbank ltration (and groundwater mountain) at Hardwald. Unfortunately, the importance of the activated charcoal filter could not be assessed adequately because of matrix e ects which made it dicult to compare the groundwater and drinking water sample directly. Based on the intensity, interferences and the availability of MS/MS information, a selection of nontargets for further structure elucidation was made. The investigation revealed that the groundwater and drinking water samples were almost free of detectable nontargets. Only four nontargets were suitable for further structure elucidation and their chemical formulas were found to be C6H8NO2I, C16H30O4, C10H5O3I and C18H22O6. For each candidate, several structural suggestions were made but no unambiguous decision could be made.