This chapter investigates the spatiotemporal distribution, sources, and health risks of groundwater nitrate pollution under land use changes in the selected area of the northern Qinling Mountains, focusing on Qishan–Mei–Zhouzhi–Huyi region. For this study, 64 groundwater samples were collected and analyzed to assess hydrochemical characteristics and nitrate concentrations, alongside the use of Piper diagrams to classify groundwater types. The Random Forest model identifies dominant factors influencing nitrate levels, while the Bayesian stable isotope mixing model (MixSIAR) quantifies the contributions of nitrate sources such as soil nitrogen, fertilizers, and sewage. Health risk assessment employs deterministic and stochastic (Monte Carlo simulation) approaches to evaluate non-carcinogenic risks for adults and children, with sensitivity analysis to address parameter uncertainties. The chapter highlights the interplay between land use patterns, particularly farmland and residential areas, and groundwater nitrate pollution, providing insights for sustainable land and water management. The findings highlight the need for targeted mitigation strategies to reduce health risks associated with nitrate contamination.