Water treatment facilities in Nigeria face significant challenges due to inadequate infrastructure and financial resources. The study employs a difference-in-differences (DiD) econometric model to assess cost-efficiency. The DiD approach will compare changes in costs and efficiency across treated versus untreated facilities pre- and post-intervention. A preliminary analysis revealed that the DiD method accurately captured the impact of government subsidies on reducing operational costs by $10 per capita, with a confidence interval of ±$5. The DiD model demonstrated its effectiveness in measuring cost-effectiveness transitions post-intervention compared to pre-intervention levels. Further research should explore scalability and sustainability of the identified cost-reduction strategies. Water treatment, Nigeria, Cost-effectiveness, Difference-in-Differences (DiD), Econometrics