Within the global transition to sustainable urban water management, Dutch polder cities are also contemplating revitalising their water traditions. One of the keys to this task is to integrate water management into urban design, which is explored but not yet practically instrumentalized in the urban design process. This article introduces the concept of hybridity and develops a Hybridity Design Approach as an interdisciplinary methodology to explore the possibility of realising the extreme low impact Closed City Concept. Integration of the water environment and urban space needs interdisciplinary cooperation and sharing knowledge, as well as an innovative way of thinking about water-resilient urban design, maximising the landscape quality of a polder city while minimising its hydrological footprint in the region. Effective visualisation tools and techniques for this collaborative design process are developed and tested in the area of Zevenkamp in Rotterdam.

The hydrological cycle crosses three environments: the geosphere, the biosphere, and the technosphere. The geosphere is the collective name for lithosphere, hydrosphere and atmosphere. The technosphere is the part of environment composed by wide variety of technological artefacts and the biosphere is composed of all ecosystems. These spheres can’t be analyzed and described separately but need to be understood as one hybrid space. Hybridity is defined as a system that is composed out of several separated systems drinking and sewer water is connected to the natural system because it also discharges rainwater. In order to be able to intervene in this system it needs to be described and analyzed to be understood. Moreover, it needs to be linked to urban space and quality to be able to harmonize urban development and water management. The urgency at the core of this study is the contemporary issue of climate change and consequently the changing hydrological cycle. To deal with pluvial flooding in cities, reduce energy use by introducing decentralized sewer systems, improve water quality by separated sewer systems and introducing blue-green infrastructure this study aims to give proper understanding and means to improve the water system, the water chain and urban quality simultaneously. One of the concepts to deal with water excess and energy use reduction is the application of a decentralized water circulation system called "Closed City", which was presented in 2005. Closed City is defined as “a city that does not have adverse effects on its surroundings, such as water depletion or emission of pollution”. This proposal is to improve the water storage and water purification capacity of cities, to store and recycle rainwater and sewage. This is believed possible by creating a self-sustaining water circulation system that responds to water shortages and floods.