Despite advances in proximal and remote sensing of surface-water reservoirs, many regions still lack reliable and timely storage records due to sparse or non-public gauging that limits sensor validation. In this study, we evaluate the potential of synthetic-aperture radar (SAR) to monitor storage dynamics of the Latyan Dam in Iran, a key drinking water supply reservoir. Sentinel-1A imagery was processed in Google Earth Engine to delineate reservoir water extent by sweeping a backscatter threshold T (dB), which was then converted to storage using the design storage-area-elevation curve. Validation was performed against a sparse time series of reported storage values compiled from online media sources. Optimal agreement with reference data was obtained for T = − 18 dB, yielding strong performance metrics (Kling-Gupta efficiency, coefficient of determination, and root mean square error) across the full period of analysis. Results highlight that SAR-derived water extents provide a reliable basis for reconstructing multi-year storage variations in reservoirs where conventional monitoring is limited. The approach illustrates a transferable and cost-effective framework for strengthening water governance and drought management in data-scarce regions.