**4. Conclusions**

In this study, the main aim was to investigate groundwater quality through the combination of the Schoeller diagram and the Canadian Groundwater Quality Index (GWQI). This study tried to evaluate and analyze the water quality in Ottawa city in Ontario, Canada, based on long-term qualitative data from 15 sample wells between 2002 and 2019. The classified water quality maps of each chemical parameter were prepared using the kriging method based on a fuzzy set in the GIS environment. The obtained results showed that, based on the Schoeller diagram, most of the studied wells were located in good to acceptable quality regions regarding drinking purposes. According to the Schoeller classification map of groundwater resources, the acceptable class, with 56.51% of the aquifer area, and the non-potable class, with 3.70% of the aquifer area, made up the highest and lowest portions of the aquifer, respectively. Moreover, according to the GWQI water quality classification map results, 79.18% of the wells were in the fair to excellent range, and 10% were in the poor range. Finally, the results of assessing the integrated Schoeller and GWQI water quality classification map used for drinking purposes showed that, based on the values of these two methods, the water quality in the central areas and near-west areas were categorized into excellent and good classes, and from the central regions to the east, the water quality had gradually decreased. Moreover, the transferability of the proposed method and results can be discussed in light of the obtained outcomes. Our approach integrated the GWQI index, Schoeller diagram, and GIS to develop a model that can be utilized for agricultural, industrial, and environmental purposes by including several chemical parameters. The GWQI index enabled us to expand the model to encompass other water quality diagrams, such as Wilcox and Piper. Moreover, our study's reliability and

transparency provide significant insights for researchers and decision-makers to analyze and make informed decisions about the quality of drinking water. These results show that the proposed method is transferable to more extensive case studies, providing valuable insights for various water quality applications.

**Author Contributions:** Conceptualization: A.N., F.R. and H.B.; methodology: A.N. and F.R.; software: A.N.; validation, F.R.; formal analysis, H.B. and A.N.; data curation, A.N. and F.R., writing—original draft preparation, A.N. and H.B.; writing—review and editing, H.B.; visualization, A.N., F.R. and H.B.; supervision: H.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data available on request due to restrictions e.g., privacy or ethical.

**Conflicts of Interest:** The authors declare no conflict of interest.
