The left bank watershed from Wuhan to Hukou, as one of the key three-tier sub-basins in the middle reaches of the Yangtze River, encompasses several major urban centers, including Wuhan, Xiaogan, Huanggang, and Suizhou. It provides vital water resources to local population. Consequently, ensuring drinking water security for both human consumption and livestock welfare is of paramount importance. Dynamic changes in water area directly reflect water supply situation. Precise monitoring on water area in reservoirs is crucial for accurate management and effective allocation of water resource, as well as the protection on water ecological environment and avoiding water disasters. This study utilized time series radar images from Sentinel-1 A/B and the Edge Otsu water area extraction algorithm to monitor the water area changes in the drinking water source reservoirs (DWSR) within the catchment from 2018 to 2021. The accuracy evaluation results indicated that the overall precision of water area extraction exceeds 0.95. We employed the PELT (pruned exact linear time) mutation detection algorithm to identify abrupt temporal changes (drastically changed, exceeding normally seasonal variations) in water area of the DWSR within the basin from 2018 to 2021. The results showed that from 2018 to 2019, the DWSR water areas in the basin shranked by approximately 33%. From October 2019 to June 2020, the water areas remained at a relatively low and stable level. Starting from July 2020, the water areas rapidly increased and recovered to the high levels seen in 2018, followed by continued fluctuations. Further analysis using the standardized precipitation evapotranspiration index revealed that the basin experienced a drought event from 2018 to 2019, followed by a wet event in 2020. These climatic conditions were associated with the observed significant changes in water area. This study demonstrates the capability of Sentinel-1 dual satellite observations to monitor large-scale changes in water areas, particularly in capturing rapid and precise responses to environmental changes. Our findings underscored the importance and urgency of enhancing the fine-scale monitoring and management of DWSR under the influence of climate change and extreme events. The results provided a scientific basis for improving water resource management and ecological protection, optimizing water resource allocation, and ensuring the security of regional drinking water resources.