This contribution focuses on the application of non-targetscreening by liquid chromatography-high resolution massspectrometry (LC-HRMS) as a tool in routine water analysis. From the perspective of water suppliers, comprehensivemonitoring strategies are required to ensure good water quality.We will illustrate the strengths of the non-target approachesbased on three chosen case studies. In principal, the non-targetanalysis enables monitoring approaches which also coverunknown or unexpected contaminants. The archive function ofHRMS data comprises various benefits such as retrospectivescreening and also allows determining concentrations in asemi-quantitative way. Temporal prioritization in combinationwith multivariate statistics emerged as helpful strategy forthe detection of new contaminants. This is exemplified for the identification of a spill event in river water. The spatialsampling information, on the other hand, allows the localization of possible sources of contamination. Prioritization basedon the analytical request reduces thousands of signals to fewinteresting candidates which increases the success rate duringthe identification. By such measures, it was possible to provethat a groundwater contamination is caused by an industrialwaste water treatment plant. For the evaluation of processes for water treatment, identification and quantification of individualcontaminants is not always of major interest. However,sophisticated strategies are needed to compare the purificationefficiency of new technologies to already established ones.Here we evaluated the effectiveness of the fourth treatment stepbased on activated carbon filtration in waste water treatmentplants.