The potential of rainwater harvesting and greywater recycling as an alternative domestic water resource in Bahnstadt-Heidelberg, Germany

Many German cities are developing infrastructure featuring green roofs for climate resilience. Green roofs can be integrated with rainwater harvesting and greywater recycling to reuse household water. However, it encounters several challenges. This study was conducted in Banhstadt-Heidelberg, Germany, to estimate domestic water consumption patterns, evaluate the potential of rainwater harvesting from green roofs, and assess the public acceptability of greywater recycling. The primary data were collected from 361 Bahnstadt residents through the questionnaire to estimate water consumption. The non-potable water demand in Bahnstadt was estimated at 228 m(3)/day for 5,700 Bahnstadt residents. The harvestable rainfall volume was 16,017.58 m(3)/year. When rainwater supply was compared to water demand, the potential for rooftop rainwater harvesting was 19.25%. This value indicates that the amount of rainwater collected is less than that of non-potable water required per year. To meet the demand, rainwater harvesting will need to be supplemented with treated greywater. However, only 20.78% of respondents are willing to install a greywater recycling system, mostly because of public health concerns. Overall, this study shows the tendencies toward having green roofs with integrated rainwater harvesting and greywater recycling for the possible account of water saving.