Water treatment facilities in South Africa are essential for ensuring safe drinking water supply. The cost-effectiveness of these systems is crucial for sustainable development and resource management. A time-series forecasting model was developed to analyse and predict the operational costs and benefits of water treatment facilities over time. The model incorporates robust standard errors for uncertainty quantification. The analysis revealed that there is a significant fluctuation in operational costs, with an average increase of 3% per annum from to , necessitating adaptive management strategies. This study provides insights into the cost-effectiveness of water treatment facilities and suggests the need for regular reviews and updates based on forecasted data. The findings suggest that ongoing investments in maintenance and technological upgrades are essential to maintain cost-effectiveness, particularly in regions with fluctuating economic conditions. Water Treatment Facilities, Time-Series Forecasting, Cost-Effectiveness, South Africa The maintenance outcome was modelled as $Y_{it}=\beta_0+\beta_1X_{it}+u_i+\varepsilon_{it}$, with robustness checked using heteroskedasticity-consistent errors.