## 2 Integrated and Decentralised Urban Water Management: A Resilient Approach
### Quality and Treatment of Water for Non-Potable Reuse
They can include one or more of the following stages [49]: (a) sedimentation/flotation: use of settling tanks to remove solid particles; (b) screening: filtering of large particles; (c) fine mechanical filtration: membrane filtration to remove fine particles; (d) biological treatment: aeration to promote the biological decomposition of organic matter; (e) chemical treatment: use of chemical agents, such as chlorine, for precipitation and disinfection; and (f) disinfection by ultraviolet radiation: elimination of pathogenic microorganisms. An effective greywater treatment system must include biological and filtration stages and disinfection processes to guarantee stable final quality. The installation of chlorine dosing in the storage tank is recommended to ensure that the treated water is free of pathogenic microorganisms and that the residual chlorine is maintained throughout the storage period [50], thus guaranteeing the quality and safety of the treated water. Treatment systems, which can be direct, short retention, basic physicochemical, biological, or biomechanical, are selected based on the specific needs of each application and considerations of sustainability and environmental impact [49]. In addition to greywater treatment, it is crucial to pay attention to rainwater utilisation systems, considering their purification and treatment. According to the technical specification ANQIP ETA 0701, 2022, in Portugal, these treatments include the following: (a) basic treatments by filtration (in the upstream filter) and by sedimentation and flotation (in the cistern), providing initial purification; (b) for activities such as watering green areas, washing pavements, and flushing toilets, rainwater may not require any additional treatment; (c) in cases of suspected or detected microbiological contamination, disinfection with appropriate treatment is recommended; and (d) when the catchment area includes polluted zones, such as vehicle traffic areas, appropriate supplementary treatments such as flocculation and/or disinfection should be considered. The following tables show the regenerated water quality standards for different uses and appropriate treatment levels (Tables 5-7). By implementing appropriate treatment systems, it is possible to ensure the safe and efficient use of grey and rainwater for non-potable purposes, contributing to the sustainable management of water resources. The comparative analysis presented in Tables 5 and 6 shows the differences in quality requirements for different contexts, including Portuguese (urban use and in buildings), British, Singaporean, and Brazilian regulations, making it easier to analyse national regulations. It is important to stress that infiltration into the ground or direct discharge into water bodies requires a licence from the relevant river basin district administration, under current legislation, for both reclaimed and non-reclaimed water [48]. Ecosystem support is assessed on a case-by-case basis, taking into account the ecological status and the respective support parameters, as established in Decree-Law no. 119, 2019.