Expanding the exergy concept to the urban water cycle

The world is urbanizing fast and this increases the pressure on available resources. In a world of cities, it is therefore crucial to take a new look at the way urban systems function: where do the resources come from and where do the wastes end up? It is essential to find ways to minimize urban impacts on resource depletion and environmental impacts and also to improve cycles within the systems. Energy and water cycles are vital to support urban life. Over the last decades, important advances have been made separately in the field of integrated water management and energy efficiency in urban areas. However, for urban planning purposes a shared framework is required that allows planners to model and understand the dynamics of the broader system to achieve an integrated management of the resources. Natural energy and water cycles are modified by metabolic profiles of the cities. The metabolic profile varies with the local resource availability and the level of technological development. To cope with this complexity, the concept of Exergy, based on Thermodynamic laws, and defined as the non-used fraction of energy, has been used to understand the energy cycle in the built environment. This will lead to new approaches towards urban planning and better resources use. This paper aims to find out if the exergy concept can be expanded to the water cycle defined as the use of the non-used water(-fraction). This way the cycle can be optimized and closed at a high efficiency level. In order to achieve this, we want to study to what extend the energy and water cycles are comparable, and how they can learn from each other in order to optimize their management