Developing high-quality regional integration requires a good-quality water environment. In this study, the impact of formal and informal environmental regulation (FIER) on water environment governance performance (WEP) is examined using a fixed-effects model and spatial Durbin model with a panel data sample of 281 cities from 2011 to 2022. It is found that (i) there is an inverted U-shaped relationship between FIER and WEP, which is first promoted and then inhibited and remains significant after endogeneity exploration and multiple robustness tests; (ii) the pressure of economic growth has weakened this elationship, while the digital economy has strengthened it; and (iii) further analysis reveals that there is an inverted U-shaped relationship between the local and spillover effects of FIER on WEP. Therefore, WEP can be improved by dynamically adjusting the intensity of FIER, optimizing the appraisal orientation of local governments, and accelerating the integration of digital economy and environmental governance