## 2 Integrated and Decentralised Urban Water Management: A Resilient Approach  
It is essential to target the right type of water for each use, guaranteeing the quality required for its intended purpose (fit-for-purpose) [41]. This concept refers to the treatment of water to a quality level appropriate for its intended use, ensuring efficiency without unnecessary overtreatment. Among the functions that normally require water in the daily lives of different types of consumer activities, various demands do not require water with potability standards, competing with more noble uses, such as human consumption. For example, the average daily consumption of water per inhabitant in Portugal is approximately 195 L [42], while only 20 L are considered the minimum necessary to meet the World Health Organisation (WHO) guidelines for drinking water--essential for human health and hygiene [43]. This emphasises the importance of conserving and using water resources efficiently. Integrated and decentralised urban water management aims to respond to these challenges by promoting a holistic vision that prioritises resilience. Based on the optimisation and reuse of water resources, this approach aims to develop a model that balances water supply and demand alternatives for non-potable uses, considering integrated water efficiency solutions, circular economy, and natural processes. Several sustainable solutions and technologies are available, such as NbSs, which support decentralised water treatment and reuse; compact greywater treatment or regeneration systems for residential use, which enable significant savings in drinking water; and, at the limit, water desalination, which is effective in regions near the sea with limited access to freshwater. The methodology proposed for this management is shown in Figure 1, which promotes circularity and efficiency at different scales, from individual buildings to urban communities, managing water sustainably from abstraction to its reintroduction into the hydrological cycle. Demand management includes strategies to promote water efficiency in the built environment, such as reducing consumption, controlling losses, using efficient devices, and raising user awareness. In addition, segmenting consumption according to its purpose contributes to more effective management of the resource, as highlighted in Table 1. Water supply management is also an important part of the process, involving the use of alternative sources, such as rainwater and groundwater, and the use of treated wastewater. These alternative sources help to reduce dependence on drinking water and promote the sustainability of water supplies. This approach aims to optimise the water cycle, maximise the use of resources, and minimise environmental impact while protecting public health. In short, the proposedresilient approach is not only a response to current challenges, but also a vision for the future, ensuring the adaptation and sustainability of urban water infrastructures. Table 1 provides a succinct analysis of the possible options for utilising the different types of segregated water. The separation of flows such as urine, faeces, greywater and rainwater offers opportunities for efficient and economical resource recovery, avoiding unnecessary investment in treatment. This approach is particularly attractive for decentralised solutions, as they are close to the source of the effluent. This approach should be considered whenever possible, especially for stormwater and greywater, which provide