Background/Motivation

Austrian cities are increasingly affected by heatwaves and droughts due to climate change. Green infrastructures (GI), such as street trees, parks, and green spaces, play an essential role in cooling urban areas, supporting biodiversity, and enhancing quality of life. However, during dry periods, these infrastructures require significant amounts of water.

At the same time, regional groundwater levels are declining considerably, and projections indicate that water resources could decrease by up to 23% by 2050 while demand continues to rise. The use of treated greywater as an alternative and continuously available irrigation source therefore offers substantial potential for saving drinking water and stabilising groundwater levels.

Contents and goals

The GRAUfürGRÜN-BLAU project is the first in Austria to investigate the possibility of using treated greywater from residential buildings not only internally but also across jurisdictional boundaries for irrigating public green spaces and contributing to groundwater recharge. Previous projects such as "Queen Gudrun" or "greenWATERrecycling" were limited to the private realm; cross-sectoral use for public spaces has not yet been implemented.

Methodical Approach

Using two demonstration sites in Vienna (Kauergasse 2 and Pogrelzstraße 8), the project will analyse water quality, develop technological interface solutions, examine legal and organisational frameworks, and assess ecological, economic, and social impacts. Surplus treated greywater will be infiltrated into the soil via tree pits and infiltration basins to support groundwater recharge.

Methodologically, the project combines water analyses, column tests for filtration effects, potential assessments, procedural and legal analyses, acceptance studies, and communication and dissemination measures.

Expected Results

The project develops a system solution at the interface between private water treatment and public use, complemented by monitoring, risk assessment, and scalable guidelines. It addresses technological, legal, and organisational challenges, such as responsibilities, approval processes, and requirements for water quality and hygiene. By actively involving all stakeholders, it strengthens societal acceptance and administrative feasibility.

Project management

GRÜNSTATTGRAU GmbH

Project or cooperation partners

• GEBE-STREBEL GmbH
• Grünplan Landschaftsarchitekten
• ÖGLA Medien GmbH
• Schöberl & Pöll GmbH
• BOKU University Institute of Sanitary Engineering and Water Pollution Control (ISIG)

GRÜNSTATTGRAU
Favoritenstraße 50
A-1040 Vienna
Tel.: +43 (650) 634 96 31
E-mail: office@gruenstattgrau.at
Web: gruenstattgrau.at/projekt/grau-fuer-gruen-blau/