The centroided data (i.e. river water samples measured via Orbitrap) was processed according to the steps shown in figure . The data was first screened for potential suspects, which were obtained from the publication of the dataset. This list comprised of 816 phar-maceutical compounds from which the InChIKeys were used to setup a suspect list through the jHRMS toolbox (Section S1.5). This generated suspect list contained the positive and negative merged spectra, when found in the database, for each of the 816 compounds. The merged part entails that, if a compound has multiple spectra for an ionization mode, the MS2 information will be combined into a single entry. With this suspect list, suspect screening from the Universal Library Search Algorithm (ULSA) was performed with a mass tolerance of 0.05 Da, a minimum precursor intensity of 1000 counts, a retention width of 0.05 minutes, and a maximum isotopic tree depth of 5. These parameters were selected based on previously processed data sets with suspect screening. Details on the algorithm can be found in section S1.5. Subsequently, the suspect presence across samples was obtained by performing suspect screening alignment (Section S1.6). Here, based on a set of criteria, the best matches for each suspect are obtained across all the samples. The set criteria where a minimum precursor intensity of 10,000 counts and a minimum of 1 detected fragment. For this case, due to the lack of a retention time and a unknown/non-optimized match factor tolerance, the retention time tolerance and minimum match factor criteria were disregarded.