<p>Understanding the hydrogeology of karst aquifers is essential for developing a comprehensive drinking-water safety plan for the Hashtgerd Basin in north Iran. This study investigates the development and dynamics of karst aquifers and their interaction with alluvial aquifers in the region, which is crucial for ensuring sustainable water resources. Approximately 15% of the basin is covered by karst rocks, supplying 30% of the area’s drinking water. The hydrodynamical, hydrochemical, and isotopic properties of water from six springs, four Qanats, and four alluvial wells during wet and dry seasons are analyzed. Findings indicate that the predominant water types in all samples are calcium and magnesium-bicarbonate, resulting from the dissolution of calcite and dolomite. A linear relationship (close to the local meteoric water line) was found between δ¹⁸O and δ²H contents of precipitation, surface water, karst water, and alluvial water, with ranges from –10 to +2‰ and from –70 to +7‰, respectively (vs Vienna Standard Mean Ocean Water). No clear effect of evaporation processes on water isotopic content was detected. Hydrograph analysis suggests short water residence times (a few months) in the karst aquifers. The study concludes that pumping from new wells in the downstream alluvial aquifer could damage karst springs, as some of the karst water discharges into the alluvium. These findings provide critical insights for the sustainable management of the region’s water resources.</p>