The present situation and pollution sources of underground drinking water in Zhangjiakou, China.

To evaluate the current situation of groundwater quality for drinking water, Zhangjiakou was selected as a typical example. The comprehensive water quality identification index method and an improved fuzzy comprehensive evaluation method were employed to assess the water quality, while a matrix factor model was utilized to explore the sources of groundwater constituents. The results indicate that the groundwater in the upstream urban area is primarily affected by nitrate pollution, and its quality is inferior to that of the downstream Yaozhanbu water source. Overall, the water quality of the water source area was excellent, with the best groundwater quality recorded in 2022. The material composition of groundwater in the Taobeiying and Gushi water source areas was predominantly derived from agricultural activities and rural living. Conversely, the downstream water source area is chiefly impacted by urban development, with the material composition primarily associated with pesticide application, industrial wastewater discharge, and municipal sewage. Pesticide residues have emerged as the principal potential pollution source for local drinking water sources. Although the quality of underground drinking water sources in Zhangjiakou City is commendable, they remain at risk of nitrate pollution and are significantly influenced by agricultural activities.