Sophisticated water-wastewater systems contribute significantly to public health, but their operation is tied to significant energy consumption and their construction to material-intensive, long-lasting infrastructures. The systems are also characterized by an inability to effectively and efficiently recover nutrients. Separating wastewater into warm and lightly polluted greywater and nutrient-rich blackwater at the source, supplemented with organic municipal solid wastes, is often seen as an option to enhance resource and energy efficiency. This study compares three different system alternatives with the status quo, using the Integrative Concept of Sustainability as a methodological backbone. The system alternatives differ in the technological design of treating the separated wastewater flows. The least invasive system change focusses on the separation of wastewater at the source while the current pipeline system and central treatment plant are still in use. The most elaborate option takes the current wastewater system out of operation completely and shows the highest potential to enhance resource and energy efficiency. However, this option could face the lowest acceptance of all of the options, including status quo, and, compared to the status quo, has higher costs.