Project

Due to climate change, water‑sensitive urban development with blue‑green infrastructure is gaining importance as heatwaves, droughts, and heavy rainfalls are increasing. National strategies and initiatives at state level, as well as the revised EU Urban Wastewater Treatment Directive, call for integrated municipal planning to prioritize blue and green solutions wherever possible. Blue‑green infrastructure mitigates extreme events through temporary water retention, reduces surface runoff, increases evaporative cooling, strengthens biodiversity, and enhances the attractiveness and quality of life in urban areas.

Delivering these effects requires a reliable supply with water even during dry periods. Drinking‑water quality is not required for this purpose and should be avoided as much as possible given regional scarcity. Therefore, a wide range of alternative sources are available in urban areas, whose suitability depends on availability, quality, environmental risks and water‑regulatory conditions:

• collected stormwater,
• greywater (e.g., showers, hand basins),
  
• industrial effluents,
• condensate from air‑conditioning systems,
• discharge from water features/fountains,
• drainage water/groundwater storage,
• surface waters (possibly with temporal restrictions),
• local groundwater resources,
• treated municipal wastewater,
• legacy service‑water infrastructure.

In particular, the quality of treated wastewater varies with the composition of dischargers to the sewer and the treatment processes used. Contaminant loads and entry pathways differ depending on the source, treatment, and irrigation regime, and thus potential risks to soil, groundwater, and surface waters also change. At the same time, the requirements for storage and treatment technologies vary depending on the respective use case.

In this context, there is a need to systematically identify and assess available water sources and irrigation concepts - ecologically, legally, organizationally, and economically - in order to set robust priorities and enable the supply of blue‑green infrastructure using non‑potable water resources. The project “Wasser für blau-grün“ addresses this.

The project “Wasser für blau-grün“ analyzes the possibilities for supplying blue-green infrastructures with non-potable water sources and develops a consolidated assessment and information framework. To this end, technical, ecological, economic, and legal aspects are systematically integrated.

• Concepts and sources: Description of relevant water sources (e.g., rainwater, treated municipal wastewater, local groundwater and surface waters, sub-streams such as greywater) and their typical contaminant loads as well as requirements for storage and treatment.
• Substance-flow balance: Pathway-specific, model-based assessment of the loads entering the environment to evaluate potential risks to groundwater or surface waters.
• Economic considerations: Comparison of investment and operating costs under typical boundary conditions; allocation of costs and responsibilities among stakeholders.
• Framework conditions: Analysis of organizational options and the legal framework (including EU Regulation 2020/741, the Federal Water Act, and the Drinking Water and Groundwater Ordinances), including implementation barriers and potential needs for adaptation.
• Evaluation: Integration of the results to assess the concepts (environmental impact, feasibility, and costs).
• Transfer: An information concept and guidance for municipalities to develop, evaluate, and implement suitable solutions. The involvement of key stakeholders is planned.

The aim is to describe robust options for action and prioritized irrigation concepts for a safe, efficient, and environmentally compatible water supply for urban blue‑green infrastructure.

September 2025 until September 2027

• Funded by the State of Baden‑Württemberg: Baden‑Württemberg Ministry for the Environment, Climate and Energy Sector

• Prof. Dr. Kristian Fischer, SZA Schilling, Zutt & Anschütz Rechtsanwaltsgesellschaft mbH, Mannheim