## 5 Discussion  
As we face the emerging challenges related to water availability, the pressing need to rethink the urban water cycle and adopt innovative and integrated approaches to its management becomes evident. The transition towards more sustainable and water-sensitive urban communities requires a holistic approach that considers water efficiency, the circular economy, the resilience of urban infrastructures, and the active participation of stakeholders. This study revealed critical gaps in the regulation and implementation of practices for water circularity in urban environments. The challenges identified include the following:  
* Lack of integrated regulations for the community scale: Most regulations focus exclusively on the building scale or centralised urban systems, without clear guidelines for integrating decentralised solutions at the community level. In Portugal, for example, there is a distinction between DL 119/2019, which regulates the reuse of regenerated water for outdoor uses, and ETA 0905, which applies exclusively to buildings. This regulatory fragmentation makes it difficult to implement integrated approaches that consider both buildings and the urban environment in which they are located. * Divergence between non-potable water quality criteria: National and international regulations have different requirements for treated wastewater and rainwater, reflecting specific regulatory priorities and local conditions. Countries such as the United Kingdom, Portugal, and Singapore have more restrictive standards for different uses, while Brazil, despite establishing quality requirements, does not differentiate specific applications, resulting in greater flexibility. However, this may require more robust treatments and additional costs, depending on the end use. * Lack of financial and regulatory incentives: Financing and regulation still prioritise conventional infrastructures, hindering the adoption of hybrid models that combine centralised and decentralised systems. Although environmental certifications play an essential role in the transition to sustainable water management, the weighting given to water efficiency in these systems is low, suggesting an underutilised potential to drive more comprehensive change. To assess the applicability of the proposed model, a case study was carried out in an urbanisation area in Portugal, demonstrating its practical feasibility. The results indicate that combined strategies, such as the use of greywater and rainwater, have great potential for reducing the demand for drinking water. In the context analysed, it was found that the use of greywater can fully meet the demand for flushing toilets, while the use of rainwater can represent around 40% of the reduction in drinking water consumption in months with a higher incidence of rainfall, making it an economically viable alternative due to lower treatment costs. In addition, the integration of blue-green infrastructure (NbSs), such as retention basins and green roofs, contributes to the water resilience of the system, offering multiple environmental and urban benefits. Harmonising these strategies aligns the model with national and international sustainable development goals, strengthening climate adaptation and water security. Given these results, public policies and urban planning strategies must evolve to encourage more sustainable practices. Harmonising technical regulations between different scales and countries can facilitate the implementation of more efficient solutions, ensuring water security and regulatory flexibility. In addition, the creation of financial incentives, subsidies for decentralised technologies, and specific certifications for urban communities can accelerate the transition to hybrid water management models. Incorporating these systems into master plans and building regulations would contribute to the efficient use of water resources, reducing pressure on public networks and operating costs in the long term.