Through the energy transition and requirements on circular economy, significant progress has been made regarding the usage of alternative forms of energy and the comprehension of wastes as valuable resource. However, in many cases, both the energy and the waste sector are being optimized without integrating the water and waste water sector and without considering potential interdependencies between the systems. The conventional water and waste water infrastructure is considered highly inflexible due to its capital intensiveness, form of organization and behavioral patterns regarding sanitation. Therefore, adequate reaction to demographic, climatic and ecological changes poses a special challenge.

Greenfield pilot projects, which combine the components of water, energy and waste intelligently, demonstrate the potential of designing this nexus of resources sustainably. By separating the different partial flows, they can be treated more energy and resource efficiently. Additionally, by combining flows of different sectors, e.g. toilet blackwater and organic kitchen waste, energy can be generated jointly and resource efficiently. Further, through the concentration of nutrients in the individual partial flows, valuable resources, like phosphorus, can be recovered.

Compared to the energy and waste sector, the debates about the necessary reconstruction measures have just begun in the water sector.  In isolated cases, a change of paradigm already takes place but there is a lack of projects designing the nexus outside of new development areas for the building stock and on district level. Therefore, the aim of this dissertation is to detect possible sustainability deficits of the conventional water and energy system in the building stock, to determine the potential of an alternative system regarding water and energy resources and to analyze the drivers and barriers of a transformation towards an alternative system. By means of different scenarios, possible target systems and associated transformation paths for a selected model settlement are developed and assessed with the integrative concept of sustainable development.