In recent years

China has made significant strides in water environmental protection

resulting in continuous improvements of water quality. However

challenges persist. This study analyzes the impact of water resources tax reform on water quality. Using the entropy method

a synthetic water quality index is constructed based on provincial panel data from2010 to 2022. The study then applies a multi-period difference-in-differences(DID) model to evaluate the effects of water resources tax reform on water quality. Two robustness tests are conducted: one by creating synthetic treatment and control groups

and another by randomly advancing the policy implementation date. The moderation effect is tested to explore the mechanism through which the water resources tax pilot policy influences water quality. Additionally

a heterogeneity analy'sis investigates regional variations in the policys effectiveness. The results show that the water resources tax pilot policy has a significant positive effect on water quality

which is further enhanced by increased fixed asset investments in water conservancy

environmental protection

and public infrastructure. Based on these findings

this paper offers policy recommendations

including the rational use of water resources tax revenues

strengthening the guiding and incentive roles of the water resources tax

and promoting the synergistic effect of the tax alongside other related policies.