The latest progress in information and communication technology (ICT) and the Internet of Things (IoT) have opened up new opportunities for real-time monitoring and controlling of cities’ structures, infrastructures, and services. In this context, smart water management technology provides the data and tools to help users more effectively manage water usage. Data collected with smart water devices are being integrated with building management systems to show how much water is used by occupants as well as to identify the consumption areas to use water more efficiently. By this approach, smart buildings represent an innovative solution that enhances a city’s sustainability and contributes to overcoming environmental challenges due to increasing population and climate change. One of the main challenges is resource-saving and recovery. Water is an all-important need of all living beings, and the concerns of its scarcity impose a transition to innovative and sustainable management starting from the building scale. Thus, this manuscript aims to provide an updated and valuable overview for researchers, consumers, and stakeholders regarding implementing smart and sustainable technologies for water resource management, primarily for building-scale uses.

Nature-Based Solutions (NBS) have been proven to effectively mitigate and solve resource depletion and climate-related challenges in urban areas. The COST (Cooperation in Science and Technology) Action CA17133 entitled “Implementing nature-based solutions (NBS) for building a resourceful circular city” has established seven urban circularity challenges (UCC) that can be addressed effectively with NBS. This paper presents the outcomes of five elucidation workshops with more than 20 European experts from different backgrounds. These international workshops were used to examine the effectiveness of NBS to address UCC and foster NBS implementation towards circular urban water management. A major outcome was the identification of the two most relevant challenges for water resources in urban areas: ‘Restoring and maintaining the water cycle’ (UCC1) and ‘Water and waste treatment, recovery, and reuse’ (UCC2). s Moreover, significant synergies with ‘Nutrient recovery and reuse’, ‘Material recovery and reuse’, ‘Food and biomass production’, ‘Energy efficiency and recovery’, and ‘Building system recovery’ were identified. Additionally, the paper presents real-life case studies to demonstrate how different NBS and supporting units can contribute to the UCC. Finally, a case-based semi-quantitative assessment of the presented NBS was performed. Most notably, this paper identifies the most typically employed NBS that enable processes for UCC1 and UCC2. While current consensus is well established by experts in individual NBS, we presently highlight the potential to address UCC by combining different NBS and synergize enabling processes. This study presents a new paradigm and aims to enhance awareness on the ability of NBS to solve multiple urban circularity issues.

In urban water management, green roofs provide a sustainable solution for flood risk mitigation. Numerous studies have investigated green roof hydrologic effectiveness and the parameters that influence their operation; many have been conducted on the pilot scale, whereas only some of these have been executed on full-scale rooftop installations. Several models have been developed, but only a few have investigated the influence of green roof physical parameters on performance. From this broader context, this paper presents the results of a monitoring analysis of an extensive green roof located at the University of Calabria, Italy, in the Mediterranean climate region. To obtain this goal, the subsurface runoff coefficient, peak flow reduction, peak flow lag-time, and time to the start of runoff were evaluated at an event scale by considering a set of data collected between October 2015 and September 2016 consisting of 62 storm events. The mean value of subsurface runoff was 32.0% when considering the whole dataset, and 50.4% for 35 rainfall events (principally major than 8.0 mm); these results indicate the good hydraulic performance of this specific green roof in a Mediterranean climate, which is in agreement with other studies. A modeling approach was used to evaluate the influence of the substrate depth on green roof retention. The soil hydraulics features were first measured using a simplified evaporation method, and then modeled using HYDRUS-1D software (PC-Progress s.r.o., Prague, Czech Republic) by considering different values of soil depth (6 cm, 9 cm, 12 cm, and 15 cm) for six months under Mediterranean climate conditions. The results showed how the specific soil substrate was able to achieve a runoff volume reduction ranging from 22% to 24% by increasing the soil depth.

Conventional green roofs, although having numerous advantages, could place water resources under pressure in dry periods due to irrigation requirements. Moreover, the thermal efficiency of green roofs could decrease without irrigation, and the plants could get damaged. Therefore, this study aims to improve the efficiency of conventional green roofs by proposing a new multipurpose green roof combined with fog and dew harvesting systems. The analysis determined that the average water use of green roofs in the summer (in humid regions) is about 3.7 L/m²/day, in the Mediterranean regions about 4.5 L/m²/day, and in arid regions about 2.7 L/m²/day. During the dry season, the average fog potential in humid regions is 1.2 to 15.6 L/m²/day, Mediterranean regions between 1.6 and 4.6 L/m²/day, and arid regions between 1.8 and 11.8 L/m²/day. The average dew potential during the dry season in humid regions is 0.1 to 0.3 L/m²/day, in the Mediterranean regions is 0.2 to 0.3 L/m²/day, and in the arid regions is 0.5 to 0.7 L/m²/day. The analysis of the suggested multipurpose green roof combined with fog/dew harvesting systems, in the summer, in three different climates, show that fog harvesting could provide the total water requirement of the green roofs, and that dew harvesting by PV (photo-voltaic) panels could provide 15 to 26% of the water requirements. Moreover, it could show a higher thermal impact on the building, higher efficiency in stormwater management, less dependence on the urban water network, and greater efficiency in decreasing urban air, water, and noise pollution. Finally, the novel green roof system could consume less water due to the shaded area by mesh and solar PVs and maximize the utilization of the roof area, as solar panels could be applied on the same green roof.