Beyond nutrients: groundwater extraction and petroleum discharge as dominant drivers of water quality in China

Surface water quality in China has improved substantially over the past decade but has plateaued recently under current levels of industrial activity and nutrient (N, P, and chemical oxygen demand) discharge standards. This stagnation signals the need to identify previously underestimated drivers and actionable thresholds for achieving Sustainable Development Goal (SDG) 6.3 (clean water and sanitation). A high-resolution national water quality dataset was analyzed in this study using the random forest method, partial dependence analysis, and a modified coupling coordination degree model. Results revealed that groundwater extraction and petroleum pollution now surpass conventional nutrients in water-scarce regions and industrial clusters. The three dominant factors are per capita water resources, petroleum discharge, and groundwater usage, with thresholds for good water quality at 985 m 3 per person per year, 108 tons per year, and 25.5 × 10 8 m 3 per year, respectively; falling below these thresholds reduces water quality by 5–10%. The COVID-19 pandemic period highlighted reduction of petroleum pollutants as a key factor associated with water quality recovery. Based on these findings, a spatially differentiated management paradigm was proposed that prioritizes groundwater restoration in arid northern China, stringent petroleum control in coastal industrial clusters, and integrated water–agriculture measures in northeastern farmlands. This threshold-based, mechanism-explicit framework offers a pathway toward realizing SDGs in China, and provides a transferable methodology for other countries addressing the water–development–pollution nexus.