## 4 Results and Discussion
### Water Quality for Various Utilization
#### 4.2.3 Water Quality for Sustainable Agricultural Irrigation
PI reflects the impact of high concentrations of Na\({}^{+}\) and HCO\({}_{3}\)\({}^{-}\) in irrigation water on soil. In the study area, 12.5% of the samples had PI values above 75, classifying them as good for irrigation, while the remaining 72.5% of groundwater samples fell between 25 and 75 and were also suitable for irrigation. Spatially, areas with appropriate PI values for irrigation were found in the northeastern part of the study area. From the PS values, 37.5% of the samples posed a significant risk and should be used with caution. Spatially, samples in the central-northern region were classified as Excellent to Good or Good to Injurious, while almost all samples in the southern region fell into the Injurious to Unsatisfactory category, indicating a severe threat to irrigation water quality. In addition to single-indicator assessments, multi-indicator irrigation quality diagrams are also used to reflect the suitability of irrigation for phreatic groundwater. In this study, three diagrammatic methods, the United States Salinity Laboratory (USSL) diagram, the Wilcox diagram, and the Doneen diagram, are employed to evaluate the holistic water quality [60]. The USSL diagram, first introduced by the United States Salinity Laboratory, evaluates water quality based on the values of groundwater EC and SAR. Groundwater samples are categorized into sixteen sub-classes based on different levels of EC and SAR. As shown in Figure 7a, most samples fall within the low salinity range (S1), with one sample in the moderate salinity range (S2) and two in the very high salinity range (S4). In terms of EC, most samples are in the moderate to high range (C2-C3), with three samples in the extremely high conductivity zone (C4). Overall, three samples in the C4S2 and C4S4 regions exhibit very high irrigation risk, while a part of the sample in the C3S1 region also shows a higher irrigation water quality risk. Samples in the C2S1 region display relatively better irrigation water quality. The Wilcox diagram divides water samples into five categories based on EC and Na%, reflecting their usability for irrigation. There is significant variability in water quality across the study area, with samples distributed across each different category (Figure 7b). The proportions of the five categories, including Excellent to Good, Good to Permissible, Permissible to Doubtful, Doubtful to Unsuitable and Unsuitable, are 41.67%, 25.0%, 12.5%, 4.16%, and 16.67%, respectively. According to the Wilcox diagram, 66.67% of the samples are suitable for irrigation, while 8% have questionable usability, indicating potential sodium hazards when used for irrigation. The impact of irrigation water quality on soil can be illustrated using Figure 7c. This diagram categorizes water samples into three classes based on total concentration and PI, using 25% and 75% tolerance lines. Most samples fall into Class 1, indicating minimal harm to soil. Three samples are in Class 2, suggesting a moderate risk to soil, while one sample in Class 3 is considered to pose a severe potential irrigation risk to local soil. Figure 7: The irrigation water quality demonstrated by (**a**) USSL diagram, (**b**) Wilcox diagram, and (**c**) Doneen diagram.