This study highlights that sustainable groundwater management in arid regions hinges on using vulnerability models to guide protective policies, ensure water security, and advance Sustainable Development Goal (SDG 6) on clean water and sanitation. The research evaluates the vulnerability of the unconfined alluvial aquifer in the Bam–Narmashir Plain, Kerman Province, using two parametric models: DRASTIC and SINTACS. The primary objectives were to compare the performance of these models in identifying pollution-prone zones and to assess the degree of agreement between their outputs and actual groundwater quality data. Seven key parameters were considered: depth to water table, net recharge, soil type, topography, impact of the unsaturated zone, hydraulic conductivity, and lithology. Results indicate that the central and northeastern parts of the aquifer exhibit higher vulnerability due to the high permeability of sediments and shallow groundwater depth. A comparison of the vulnerability maps generated by the two models revealed that the SINTACS model, owing to its greater flexibility in parameter weighting, offers superior discrimination of high-vulnerability zones. Model validation using nitrate concentration data showed that, although both models adequately reflect the general pattern of contamination, their correlation with actual field measurements requires improvement. Overall, the findings underscore the necessity of locally calibrating vulnerability models and implementing continuous groundwater quality monitoring for the sustainable management of water resources in the Bam–Narmashir region.