Schwammstein (Sponge Stone) – Sustainable Rainwater Management for Urban Green Spaces

© Credit: Aigner MA 28

The Schwammstein offers an efficient and innovative new solution to the market that regulates the discharge of rainwater into tree pits and green spaces.


Climate change poses significant challenges, especially for cities. The number of hot days is expected to increase, and heavy rainfall events are becoming more likely. The unpaved space in urban areas available for shady and moisture-retaining trees and green spaces is limited. Therefore, it is crucial to create optimal growth conditions for plants. The Schwammstein (Sponge Stone) will make a valuable and efficient contribution to this, by making it possible to save drinking water, improve water supply to urban vegetation, and save costs related to water consumption, disposal, and infrastructure.


The Schwammstein is a rectangular concrete block that can be seamlessly integrated into the kerb next to a tree pit. Inside a valve is opened and closed by sensors to prevent contaminated water from reaching the roots or the groundwater, while increasing the overall water supply to the plants. The power supply for the Schwammstein is independent of the grid and provided by solar energy, with a battery unit installed to bridge days or weeks without sunlight. This system saves drinking water, relieves strain on sewer infrastructure, and stores more moisture for evaporation which, in turn, helps bring down the ambient temperature.


The Schwammstein diverts more rainwater to plants, making urban vegetation healthier, and thus making a significant contribution to cooling through shading and evaporation. With widespread use of the Schwammstein, significantly more rainwater is collected in green spaces. This reduces the volume of runoff and can reduce flood damage. Furthermore, it could generate savings in stormwater sewers as pipe cross-sections in new development areas could be reduced if this rainwater management system is implemented there.

Project owner
Ulli Sima
City Councilor for Innovation, Urban Planning and Mobility
Project owner
Stadt Wien Straßenverwaltung und Straßenbau