Water scarcity is a critical constraint on sustainable development in arid and semi-arid regions of China, where growing demands from energy production, food security, and ecological protection intensify pressure on limited water resources. In Northwest China, the mismatch between water availability and sectoral demand has strengthened interdependencies and competition within the water-energy-food-ecology (WEFEco) nexus, constraining high-quality regional development. This study develops an integrated assessment framework to quantify the impacts of water resource regulation on the WEFEco nexus. Using Yulin City as a representative arid region, scenario-based simulations are conducted to evaluate how water pricing and water efficiency improvements affect sectoral water use in the energy, food, and ecological sectors, as well as associated energy and food outputs. Changes in intersectoral dependence and competition are assessed using the stress contribution rate of energy, food, and ecology on water resources (WWCR) and the Comprehensive competition index of energy, food, and ecology on water resources (CCCI). Results show that water resource regulation induces distinct sectoral responses. A 30% increase in water price reduces the overall WWCR by 8.8% relative to the baseline, with the food sector exhibiting the largest decline (13.7%), followed by the energy sector (12.5%). This scenario yields the lowest CCCI among pricing schemes (1.23), indicating reduced intersectoral competition. A 30% improvement in water efficiency leads to a larger overall WWCR reduction of 10.67%, driven primarily by decreases in the energy (16.19%) and food (14.72%) sectors, with the CCCI declining to 1.20, the lowest among efficiency scenarios. Overall, coordinated water resource regulation effectively alleviates dependence and competition within the WEFEco nexus. Simultaneous regulation of water price or efficiency in both the energy and food sectors produces the strongest synergistic effect, offering policy-relevant insights for sustainable water management in water-scarce regions.