Evaluation of the safe water optimization tool to provide evidence-based chlorination targets in surface waters: Lessons from a refugee setting in Uganda

The Safe Water Optimization Tool (SWOT) generates evidence-based point-of-distribution free residual chlorine (FRC) targets to adjust chlorine dosing by operators and ensure water quality at point-of-consumption. To investigate SWOT effectiveness in surface waters, we conducted two before-and-after mixed-method evaluations in a Uganda refugee settlement served by piped and trucked surface water systems. We surveyed 888 users on water knowledge, attitudes, and practices; collected 2768 water samples to evaluate FRC,Escherichia coli, and disinfection by-products (DBPs) concentrations; and conducted nine key-informant interviews with system operators about SWOT implementation. After baseline data collection, SWOT chlorination targets were generated, increasing point-of-distribution FRC targets from 0.2 to 0.7-0.8 mg/L and from 0.3 to 0.9 mg/L for piped and trucked systems, respectively. At endline, household point-of-consumption FRC ≥ 0.2 mg/L increased from 23 to 35% and from 8 to 42% in the two systems. With these increases, we did not observe increased chlorinated water rejection or DBPs concentrations exceeding international guidelines. Informants reported that SWOT implementation increased knowledge and capacity and improved operations. Overall, SWOT-generated chlorination targets increased chlorine dosage, which improved household water quality in surface waters although less than previously documented with groundwater sources. Additional operator support on prechlorination water treatment processes is needed to ensure maximally effective SWOT implementation for surface water sources.