## 4 Conclusions  
EEM-PARAFAC was successfully applied to track and characterise DOM at almost trace levels along the DWTP of Turin, Italy, providing information about the types of DOM and plausible chemical reactions happening along the DWTP. Even though NPOC and UVA are useful methodologies in DWTPs to rapidly check the DOM behaviour along the plant, only EEM-PARAFAC was able to properly track the trends of the different types of DOM and provided deeper layers of information regarding chemical changes. NPOC was the less sensitive technique, and changes were only observed when comparing the inlet and the outlet of each treatment line (D vs. I and M, respectively). When comparing EEM-PARAFAC with the FI, BIX, and HIX, although the indexes might offer a rapid on-line monitoring of fluorescent DOM, they do not differentiate HA-L substances from Try-L ones. Nevertheless, the BIX was shown to be a sensitive parameter to analyse fluorescence blue-shift due to decay on conjugated double bonds as a result of oxidative processes.  
In terms of processes' efficiency, the lagooning pre-treatment did not produce significant water quality improvement (site A vs. B) in terms of DOM content. Measurements of emerging contaminants by high-resolution mass spectroscopy will be required to better understand its usefulness. Differences between fluorescent and non-fluorescent DOM were observed when comparing the effect of flocculation and sedimentation (from sites D to E), since only a reduction in UVA was observed, HA-L and Try-L scores remained without significant changes. Chlorination and ozonation oxidise DOM into smaller molecules, although the first might lead to the formation of chlorinated disinfection by-products. The use of BAC was shown to reduce HA-L/Try-L content in a similar way as NaClO, the former being evidently safer.  
In future studies, we expect to analyse the reproducibility of works reporting that DOM monitoring by EEM-PARAFAC is a useful tool to predict emerging contaminants (e.g., pharmaceuticals) degradation or chlorinated disinfection by-products formation. The water treatment field certainly needs more studies to prove the reproducibility of these statements, as it will mean that extremely valuable information could be extracted from a simple and economic methodology. Furthermore, measuring DOM content at different stages of the year could be useful towards algae proliferation evaluations (one of the most challenging issues in DWTPs).  
Conceptualisation, A.A. and R.B.; methodology, I.S.; software, I.S.; formal analysis, I.S.; investigation, I.S.; resources, A.A., I.O., C.E.-O. and R.B.; writing--original draft preparation, I.S.; writing--review and editing, A.A., I.O., C.E.-O. and R.B.; supervision, A.A. and R.B.; project administration, A.A, I.O., C.E.-O. and R.B. All authors have read and agreed to the published version of the manuscript.  
The authors want to acknowledge the financial support of Spanish Ministry of Science and Innovation (MCI) for funding under the AquaEnAgri Project (Reference: PID2021-126400 OB-C31). [PERSON] also acknowledges the financial support of Generalitat Valenciana (CIAPOS/2021/311, project SANITISE).  
Not applicable.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
The authors want to thank [PERSON] for the sampling and dedication devoted to finish this work at SMAT.  
Conflicts of Interest: Author [PERSON] was employed by the company Societa Metropolitan Acque Torino S.p.A. (SMAT). The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.