This paper studies decision-making processes in relation to the implementation of innovative source-separating wastewater systems in the development area of Helsingborg called H+, and the non-implementation of the same in Stockholm Royal Seaport. Two analytical perspectives were used to identify critical organisational functions, drivers for change and the anchoring of these decisions within policy: (i) a sustainability transitions framework, and (ii) a policy trickle-down study assessing policy-concept uptake by stakeholders. Critical functions supporting implementation of source-separating systems in H+ were: common vision, leadership, cross-sectoral cooperation, and an innovative approach both within the utility and in the city administration in Helsingborg. In Stockholm, with regard to source-separating wastewater systems, there was a lack of common vision and of cross-sectoral cooperation and leadership. This was also evident in the lack of uptake by stakeholders of the policies for source separation. In Helsingborg, the main drivers for source-separating wastewater systems are increased biogas generation and improved potential for nutrient recycling. In Stockholm, these drivers have not been enough to create change, but the potential for increased heat recovery from greywater at source may be the additional driver necessary for future implementation of source-separating wastewater systems. Comparison of the stalled source-separation policy in Stockholm with a successfully implemented policy in a related field found a key criteria to be the presence of inspired individuals in positions where they had the mandate as well as the ability to create a common vision for change.