Despite management of point sources, heavy metals today remain at an elevated level in the urban environment, with diffuse sources dominating the emissions. In order to manage these pollutants, it is necessary to understand the coupling between the urban sources of heavy metals and their monitored, environmental levels, for example in aquatic sediments. In this work, we suggest a simple approach to quantitatively model Cu from its urban sources through a complex aquatic system. We apply the proposed model to Stockholm, situated between Lake Mälaren and the archipelago of the Baltic sea, and discuss data availability along with conceptual difficulties. Using literature data, we show that Cu occurs at elevated levels in the aquatic sediment close to the centre of Stockholm, Sweden.