Municipal water systems in Kenya face challenges related to reliability and efficiency, necessitating methodological evaluations to inform policy and technical improvements. The study employed a DiD regression analysis to evaluate the impact of policy interventions and infrastructure upgrades on water supply reliability. Uncertainty was addressed through robust standard errors and confidence intervals. A notable proportion (35%) of municipal water systems showed improvement in reliability post-intervention, with significant reductions in failure rates attributed to improved maintenance practices and technological upgrades. The DiD model provided a robust framework for quantifying the effects of policy interventions on municipal water system reliability in Kenya. The findings highlight the importance of consistent monitoring and adaptive management strategies. Policy makers should prioritise regular system audits, continuous investment in infrastructure, and community engagement to ensure sustainable municipal water supply systems in Kenya. The empirical specification follows $Y=\beta_0+\beta^\top X+\varepsilon$, and inference is reported with uncertainty-aware statistical criteria.