The pressure on water and energy resources, along with the transition towards new infrastructure, requires an integrated approach to achieve future-proof concepts. A nexus approach can contribute to this by including the interaction between water and energy. This is also known as a water-energy nexus (WEN). Furthermore, when considering decentralization as an ‘infrastructure pathway’, new solutions can be considered where more resources are locally used. Therefore, the circular economy principle was used as a baseline for this research, as it becomes possible to include both water and energy as important resources. There are currently various assessment frameworks that facilitate the decision-making process for different infrastructure pathways. However, it was found that these frameworks do generally not evaluation indicator that go in line with a circular economy approach.

This research presents a six-step generic assessment framework that can be used to evaluate different decentralized WEN systems. The first step was formed to give the opportunity in setting up the research scope. It has the possibility to either select one neighborhood as a study case of multiple depending on the research objectives. After that comes a modular step where it is possible to include different innovative technologies that are relevant for a more decentralized WEN system. The water- and energy balance can be modeled in the third step, providing insight into the (re)use of water- and energy sources on different temporal scales. Subsequently, the generic assessment framework contains 13 evaluation indicators that are divided into four themes: (1) water system, (2) value for people, (3) energy system, and (4) general characteristics. The last step includes stakeholder perspectives to prioritize and weigh the indicators.

A modern Dutch neighborhood with a high building density (City Nieuwegein) was used as a case study to demonstrate the generic assessment framework. Four scenarios were designed (reference, improved centralized, hybrid, and almost decentralized) to assess the impact of a neighborhood with more decentralized WEN systems. The case study results showed that more decentralization strategies improved most indicator scores. Using different decentralized WEN systems increases the collection and storage of local water- and energy resources. It was found that neighborhoods with more decentralization strategies have a higher complexity (e.g., monitoring and spatial limitations) in implementation. Moreover, the investment- and maintenance costs can be up to 51% higher compared to a neighborhood with minimal decentralized WEN systems. However, the outcomes of the six stakeholder perspectives, showed that the scenario with the highest level of decentralization was, in all cases, preferred.

The results of the case study showed that the generic assessment framework can be used to evaluate different decentralized WEN systems. The 13 evaluation indicators followed the circular economy principle as this favors future-proof concepts. Besides, the generic assessment framework included stakeholder perspectives so that it can facilitate the decision-making process of stakeholders. This framework can be further improved by including multi-objective optimization resulting in more scenarios that can be simulated. At last, more research is required for qualitative indicators that improves evaluating the different scenarios.