## 4 A Case Study
Based on the technical literature and applicable regulations [64; 65], the daily water consumption for the area's users was estimated. The residential area should accommodate around 1042 inhabitants, while the commercial and service spaces will have an average of 1534 occupants. This corresponds to an aggregate demand of approximately 205.9 m\({}^{3}\)/day of drinking water, which serves as the basis for developing a local water balance. This assessment integrated studies on diversifying the supply matrix and strategies to reduce potable water consumption in non-essential uses--as summarised in Table 9.  
The analysis shows that the daily supply of greywater (77.1 m\({}^{3}\)/day) is sufficient to meet the demand of 63.3 m\({}^{3}\)/day for flushing toilets, demonstrating the potential to reduce drinking water consumption for non-potable uses. However, reusing this water for purposes such as cleaning and irrigation requires robust treatment and quality control solutions. The availability of rainwater shows strong seasonal variability. In the rainiest months (generally from October to January), average catchment can reach approximately 75.8 m\({}^{3}\)/day, while in dry periods (from June to August), this supply drops to around 9.7 m\({}^{3}\)/day. This fluctuation highlights the need for properly selected and sized storage infrastructures, which can be integrated into the retention basin provided for in the plan, to optimise the use of this source during periods of low rainfall. Furthermore, the demand for irrigation of large green areas, which can reach 455.3 m\({}^{3}\)/day, contrasts with the demand for general cleaning (23.3 m\({}^{3}\)/day), highlighting the impact of green spaces on the water balance. In scenarios of high rainfall, disregarding irrigation, drinking water consumption can be reduced by up to 86.6 m\({}^{3}\)/day--representing a saving of approximately 42% of the 205.9 m\({}^{3}\)/day demanded. This result reinforces the viability of using greywater and rainwater for non-potable purposes, relieving pressure on resources intended for human consumption. Among the solutions highlighted, the retention basin emerges as a highly relevant blue infrastructure, contributing not only to flood management but also to mitigating the effects of seasonality on rainwater availability [18]. The adoption of nature-based solutions (NbSs), such as green roofs integrated with solar panels--which can increase retention by up to 120 L/m\({}^{2}\)[66]--combined with the implementation of efficient irrigation systems and the use of native species adapted to aridity, reinforces the overall efficiency of the water system. To optimise the sustainability of the urbanised area, an integrated and circular approach to water management is proposed, considering the synergy between centralised and decentralised systems. National and international studies show that converting wastewater into resources--through recycling and by-product recovery technologies--can significantly strengthen water security and promote urban sustainability. In this sense, the implementation of hybrid water management models, integrating the existing Wastewater Treatment \begin{table}
\begin{tabular}{l c c} \hline \hline
**Source of Water** & **Yield [m\({}^{3}\)/day]** & **Demand [m\({}^{3}\)/day]** \\ \hline Greywater & 77.1 (A) & 63 (B) \\ \hline Rainwater & & \\ Months with the highest rainfall (C) & 75.8 (D) & \\ Months with less rainfall (C) & 9.7 (D) & \\ Without irrigation (applicable to green areas) & 23.3 (E) & \\ With irrigation (applicable to green areas) & 455.3 (E) \\ \hline \hline \end{tabular}  
Notes: (A) Water from washbasins, showers, and baths. (B) Water intended for flushing toilets. (C) Precipitation data were obtained from the National Water Resources Information System for the Lis/Ribeires Cosetíras Hydrographic Basin (Meteorological Station: 15E/01 UG). (D) The catchment areas take into account 75% of the area available on the plots. (D) Water used for general cleaning (floors, washing clothes).  
\end{table}