## 3 Results and Discussion
### Groundwater Indices Based on Hydrochemical Features  
Figure 13 presents the classification of water quality for irrigation purposes. Some groundwater indices obtained in this study suggest that the Cuernavaca aquifer has a good quality for irrigation purposes. For example, the SAR index classified the groundwater as excellent, which indicates that there is no risk of sodium for irrigation. The RSC index also showed that all samples presented a good quality of water for irrigation. Based on the KR index, the groundwater of the Cuernavaca aquifer was adequate in most of the samples (84%). Figure 12: Gibbs diagram showing the source of cations and anions in the Cuernavaca aquifer at P1 ((-)-), P2 ((-)-), P3 ((-)-) y P4 ((-)-) sites. However, other groundwater indices suggest that groundwater quality is inadequate for irrigation. The SSP index showed that 65% of the samples have good water quality, mainly at P2 and P4. However, most of the samples at P1 and P3 showed an inadequate quality. [PERSON] et al. [31] reported that 53.3% of samples analyzed in alluvial aquifers in the Upper Blue Nile Basin, Ethiopia, could be considered good quality but 46.7% of the samples could be considered unsuitable. The MH index demonstrated that 56% of the samples have adequate quality at P2 and P4, but inadequate at P1 and P3. The high sodium levels found at these sampling sites could be related to weathering of Na-containing basaltic rocks. However, the content of calcium (41.93 mg/L) and magnesium (19.25 mg/L) in the groundwater of the aquifer maintains an equilibrium state. The groundwater of the Cuernavaca aquifer could be considered good quality according to the %Na. Most of the samples (56%) are within 20-40% Na. However, high sodium percentages were recorded in 38% of the samples, mainly at P1. The presence of high levels of sodium could reduce soil permeability. Similar results were obtained when using the PI index. Good water quality was observed in 56% of the samples, but it is noteworthy that 29% of the samples were within the poor-quality range (PI > 100). This groundwater quality index is related to the texture and structure of the soil. Since a high content of ions such as sodium, magnesium, calcium, and bicarbonate were found in the aquifer, the PI index also suggests that the use of groundwater for irrigation could affect the soil permeability [19]. Moreover, the high levels of bicarbonate over calcium and magnesium make groundwater unsuitable for irrigation uses. The hardness of groundwater varied from soft to very hard. This variation is related to urbanization since soft groundwater was found at P1, characterized by the presence of agricultural areas, with low population density and small settlements, while very hard groundwater was located at P2 which is characterized by a mineralized subsoil. Hardness levels found in this study could be considered normal according to that suggested by [PERSON] [49], who reports similar TH values in the groundwater of Sri Lanka. The electrical conductivity in the Cuernavaca aquifer was found between 90 and 991 \(\upmu\)S/cm. Despite this high variation, most of the samples were in a good quality range according to [PERSON]'s [50] classification (EC level between 0 and 750 mS/cm). The levels of electrical conductivity have been increasing during the last years. This increase could be also related to the loss of vegetation cover due to urbanization [51]. However, electrical conductivity in groundwater showed a satisfactory quality classification because the presence of ions (Ca\({}^{2+}\), Mg\({}^{2+}\), Na\({}^{+}\), K\({}^{+}\), Cl\({}^{-}\), HCO\({}^{3-}\), SO\({}^{2+}\), and NO\({}^{3-}\)) is within the permissible limits according to the standards of the World Health Organization  
Figure 13: Classification of water samples for irrigation purposes in the Cuernavaca aquifer. (WHO).