Municipal water systems in Rwanda have been implemented to improve public health outcomes. A systematic review using the difference-in-differences (DiD) model was conducted, focusing on existing observational studies in Rwanda. The DiD analysis revealed a significant improvement in waterborne disease incidence post-implementation of municipal water systems. The DiD method provided robust evidence for the effectiveness of municipal water systems in reducing clinical outcomes related to water-borne diseases. Future studies should consider additional variables and longitudinal data to strengthen model validity. The empirical specification follows $Y=\beta_0+\beta^\top X+\varepsilon$, and inference is reported with uncertainty-aware statistical criteria.