Urban water neutrality at different scales: CityPlan design and evaluation framework

London aims to build more than half a million households over the next 10 years to cope with the growing demand for housing in the UK. In this future scenario, urban water security levels will be threatened due to new development pressures combined with the climate emergency and exponential population growth in the city. In addition to this, there is a lack of agreement between the policy and decision-making sectors to decide what can be accepted as a sustainable urban development project and which are the physical and decision boundaries inside the city (i.e., while boroughs and wastewater zones present decision boundaries, new urban developments have physical boundaries only). In our previous work, we developed a new concept for urban Water Neutrality (WN) inside an operational framework called CityPlan to frame the concerns about rising water stresses in cities. This framework integrates spatial data with an integrated urban water management model, enabling urban design at systems level and delivering a new index that assesses possible future scenarios. Despite several studies related to WN, little evidence is yet available in the literature of how urban water neutrality can be achieved at different urban scales and if results might vary depending on the scale studied.

In this work, we expand the CityPlan framework and present an innovative evaluation approach that sets several urban indicators to be tested at different urban scales. As part of the evaluation toolkit of CityPlan, we also develop the Water Efficiency Certificate (WEC) by boroughs using two novel criteria: the Housing Age Indicator (HAI) and the Device Efficiency Score (DES). The WEC evaluates the current situation of household water consumption and can be used to support predictions of water consumption under different scenarios, to study the potential for retrofitting existing residential buildings, and to develop water-efficient households. In the end, the full development of the CityPlan framework will provide a clear vision to contextualise water neutrality in urban water systems and its key role in urban water security at different urban scales.