Green roofs (GRs) and vertical greenery systems (VGSs) can contribute certain pollutants to stormwater runoff, affecting the quality of the receiving waters. The objective of this review paper is to discuss the potential impact of these systems on the quality of urban runoff. In the green building systems section, a series of materials used in greenery systems and their specific application are presented and environmentally relevant substances that could be leached out from these materials are identified as potential pollutants. After the identification of environmentally relevant pollutants that have already been measured in urban runoff and originate from these systems, an assessment of their pathways, fate, and impact in the aquatic environment is performed. Since GRs and VGSs are already considered to be solutions for stormwater quantity and quality management in urban areas, recommendations for mitigating their environmental impact through runoff are needed. It can be concluded that special focus should be placed on measures that target the pollution source, such as optimizing GR and VGS construction practices and materials used, as well as establishing appropriate decentralized stormwater treatment measures. Both of these approaches will help to reduce or even entirely avoid the emission of relevant pollutants into the aquatic environment.

Vertical greenery systems (VGS) are promoted as a nature-based solution to mitigate the urban heat island effect. In order to ensure the long-term provision of this function, sufficiently available irrigation water is the key element. Currently, potable water is one of the main resources for irrigation of VGS. While rainwater is often mentioned as an alternative, only a few studies investigate the actual application of rainwater for irrigation. In this study a conceptual model is developed to present the processes and influencing factors for a holistic investigation of rainwater use for irrigation. In this model, five sub-modules are identified: the atmospheric, hydraulic, quality, rainwater harvesting and VGS sub-module. The conceptual model depicts which processes and influencing factors are involved in the water demand of VGS. Thus, the conceptual model supports a holistic understanding of the interrelations between the identified sub-modules and their relevance for VGS irrigation with harvested rainwater. The results of this study support the implementation of rainwater harvesting as a sustainable resource for VGS irrigation.

The application of nature-based solutions for climate change adaptation in cities has increased in recent years. To improve microclimatic conditions and to preserve the natural components of related assets, water supply is necessary. As an alternative to drinking water, stream water might serve as a natural source for irrigation. However, due to continuous urbanisation, water courses have often been banned underground in pipes or integrated in the combined sewer network, both making them not directly available for further usage. This article focuses on the perspectives of decoupling captured streams from underground infrastructure to support nature-based urban climate adaptation measures. It introduces a method to identify suitable locations for practical implementation considering the hydrological potential of the stream and the urban microclimatic sensitivity of the concerned area. The approach was applied in a case study in the north-western part of Vienna, including 16 streams with a total length of about 39 km covering an area of approximately 95 km2 with about half a million inhabitants. This work proved the general practicality of the suggested method. It also revealed that about one-third of the investigated stream lengths appears high or medium suitable to support climate adaption measures, leading to notable cost savings for irrigation (for the substitution of drinking water) and wastewater treatment. Concluding, the decoupling of captured streams could contribute to a more sustainable and nature-based urban water management. The introduced method for suitability pre-assessment is applicable with rather easily available input data, which makes it transferable to other cities.

Zusammenfassung Der Klimawandel stellt urbane Räume durch vermehrte Trockenperioden und Starkregenereignisse vor große Herausforderungen und fordert Maßnahmen, um die Lebensqualität aufrecht zu erhalten. Urbane Begrünung spielt als Klimawandelanpassungsmaßnahme eine wichtige Rolle – allerdings können Pflanzen nur bei ausreichender Bewässerung einen mikroklimatischen Kühleffekt erzielen. Aktuell wird vorrangig Trinkwasser zur Bewässerung herangezogen, was langfristig als nicht nachhaltig einzustufen ist. Im urbanen Raum stehen weitere Wasserressourcen, wie Regenwasser, Abwasser oder Grauwasser (Abwasser ohne Fäkalien) als Brauchwasser, beispielsweise zur Bewässerung, zur Verfügung. Diese Wasserressourcen haben ein großes Potenzial zur kreislauforientierten Wiedernutzung, welches jedoch in Österreich aktuell nicht ausgeschöpft wird. Daher stellt sich die Frage, inwiefern Wasserwiedernutzung in österreichischen Strategien zur Klimawandelanpassung berücksichtigt wird und welche Potenziale sich daraus ergeben. Dazu werden in diesem Artikel Strategien zur Klimawandelanpassung auf Bundes- und Landesebene analysiert, das qualitative und quantitative Potenzial von Regen- und gereinigtem Grauwasser aufgezeigt und Herausforderungen in der praktischen Umsetzung von Wasserwiedernutzung identifiziert. Die Ergebnisse zeigen, dass der Brauchwasserbedarf mit urbanen Wasserressourcen gedeckt werden kann (mit variierendem Deckungsgrad je nach Ressource) und damit eine nutzungsorientierte Verwendung dieser Ressourcen ein hohes Potenzial aufweist. Auch wird eine Brauchwasserversorgung als Teil des Maßnahmenpakets zur Anpassung an den Klimawandel gesehen. Allerdings zeigt sich, dass in der Praxis einige Herausforderungen bei der Umsetzung von und der Schaffung der Voraussetzungen für Wasserwiedernutzung gesehen werden. Diese Lücke zwischen der Vision einer klimawandelangepassten Zukunft und den identifizierten Herausforderungen in der Praxis muss geschlossen werden, um langfristig Brauchwasserbedarf – wo möglich – mit urbanen Wasserressourcen zu decken und die wertvolle Ressource Trinkwasser für den tatsächlichen Trinkwasserbedarf zu sichern.

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Energy from wastewater is increasingly recognized as a valuable, locally available renewable resource that can support the decarbonization of heating and cooling in both municipal and industrial sectors. This article highlights its diverse applications, including the supply of existing buildings, inhouse solutions, tapping treatment plant effluents, wastewater‑based cooling, and the benefits of digitalization for system monitoring and optimization. It also underscores the potential of combining wastewater heat with other renewable sources to enhance seasonal performance and system resilience. Recent real‑world projects demonstrate the technological maturity and reliability of wastewater‑based energy systems. Notable examples include the heating of the Town Hall in Tulln using approximately 100 kW of wastewater heat, and the large‑scale system at voestalpine in Linz, delivering 1 MW of heating to production areas and office spaces. Looking forward, the broader roll-out of energy from wastewater projects will depend on strengthened regional energy planning, standardized and accessible data, targeted funding schemes for feasibility studies and pilot projects, and closer collaboration between the wastewater and energy sectors. These advancements position wastewater as a key contributor to future climate‑neutral and resilient energy systems.