Urban source separation infrastructure systems have a promising potential for a more sustainable management of household food waste and wastewaters. A renewed trend of larger implementations of pilot areas with such systems is currently emerging in Northern Europe. This study investigates the drivers behind the decision of stakeholders to implement source separation systems as well as the importance of the previously existing pilot areas in the decision-making process. By means of semi-structured expert interviews, five areas with source separation were characterized and compared. It was found that the most important drivers were on the one hand governmental, especially local environmental goals and on the other hand the ambition of the utilities to gain knowledge about future wastewater management and treatment technologies. Experiences from existing smaller pilot areas were shown crucial for decisions to implement the larger pilot areas that are currently planned, as was intensive stakeholder co-operation, due to the fact that source separation systems transcend traditional boundaries between energy, waste and water sectors. The results hold implications for policy makers and municipalities initiating a transition to more sustainable wastewater management.