<p>Groundwater is a critical water resource in arid and semi-arid coal-mining regions, where mining-induced disturbances can modify aquifer conditions and degrade water quality. In this paper, hydrochemical analysis, Self-Organizing Maps (SOM), correlation analysis, and the Objective Combined Weight Water Quality Index (OCWQI) were integrated to characterize groundwater hydrochemical features, assess groundwater quality in the Dahaize coal mine area, and identify the key factors controlling water quality. Based on the Piper trilinear diagram, two dominant hydrochemical facies were identified: Ca–HCO₃ and Na–Cl. Major-ion chemistry is mainly controlled by water–rock interaction, evaporation crystallization, cation exchange, and anthropogenic inputs. Groundwater quality in the Zhiluo Group is generally poorer than that in the other aquifers. SOM and correlation analyses suggest that Na⁺, SO₄²⁻ and F⁻ are among the key parameters influencing groundwater quality and support the rationality of the OCWQI weighting. Anthropogenic activities influence groundwater hydrochemistry: elevated SO₄²⁻ in deeper groundwater shows a correlation with mining-affected zones, whereas NO₃⁻ and NH₄⁺ in shallow groundwater show patterns consistent with inputs from agricultural fertilization and domestic wastewater. This study proposes a method for evaluating the rationality of indicator weights in water quality assessment, providing a reference for groundwater quality management in coal mining areas and offering insights into water quality evolution and pollution risks in arid regions.</p>