Understanding how pollutants move and where they come from is crucial for reducing urban stormwater pollution. This study looked at different types of pollution in separate sewer systems, like road runoff and sewer sediments. They found that fine particles increased as pollutants moved through stormwater runoff. Small particles were the most mobile, while larger particles were less mobile. Heavy metals mostly came from road deposited sediments, while organic matter and nutrients came from sewer sediments. Rainfall intensity affected pollutant levels in road runoff, and sewer runoff had lower pollutant levels in rainy seasons. Overall, road runoff contributed the most particles to urban water bodies, followed by sewer sediments and roof runoff.