Analysis of hazardous events and risks using a water safety plan approach: A case study in a water supply system in a tropical Indonesian large city

A water supply system (WSS) serving six districts in a large tropical Indonesian city reported 0.04–1.84% diarrhea cases in 2023. Given the importance of safe drinking water for public health, a Water Safety Plan (WSP) based on a risk management approach from catchment to consumer tap was carried out to identify and prioritize risks within the WSS. The raw risk analysis identified 150 hazardous events classified as extreme, very high, high, and medium risk levels; and the source as having the highest overall risk, followed by the water treatment plant (WTP) and consumer points, underscoring the impact of catchment activities and operational practices on water safety. The residual risk analysis observed that control measures were effective in the transmission system, clear well, and most parts of the distribution system and customer points, but were ineffective or of uncertain at the source, intake, and WTP. Targeted improvement plans and continuous operational monitoring are thus necessary to further minimize risks and ensure safe drinking water throughout the WSS. The improvement plans addressing extreme risks, particularly in the distribution and consumer areas, should be prioritized to improve drinking water safety and support public health protection.