<![CDATA[Raw-water security in urban watersheds depends on the interaction among hydrological potential, source-water quality, and the capacity of water-supply systems to deliver reliable services. This study developed a source-to-service diagnostic framework for the Air Bengkulu Watershed, Indonesia, integrating 90% dependable flow (Q90), normative domestic water demand, actual piped-water delivery, regulatory water-quality exceedances, and event-based pollutant transport. The results showed that dependable flow substantially exceeded normative domestic water demand, whereas actual household piped-water delivery accounted for only 38.0% of the estimated demand. This ratio was interpreted as an indicator of service delivery relative to planning requirements rather than a measure of household coverage or total water availability. Across three monitoring campaigns conducted in 2025, downstream water quality consistently exceeded Class II regulatory thresholds for organic pollutants, nutrients, oil and grease, and faecal contamination indicators. Event-based calculations further demonstrated that pollutant transport varied substantially with river discharge, highlighting the limitations of assessing pollution solely through concentration measurements. The main novelty of this study lies in integrating hydrological potential, pollutant loads, flow-dependent transport, and actual water-service delivery within a unified source-to-service assessment framework. The findings emphasize the importance of risk-based pollution control, flow-synchronized water-quality monitoring, improved intake management, and treatment preparedness. The proposed framework supports more informed water-resource management without assuming that all dependable river flow is directly available for abstraction, treatment, or household distribution.]]>
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