Off-grid rainwater and greywater treatment and reuse on household level: Conceptual approach and pilot operation at the KREIS-Haus demonstration case, Switzerland

ABSTRACT KREIS-Haus, a living lab in Feldbach, Switzerland, features a novel, decentralized, closed-loop water system that combines rainwater harvesting and greywater treatment for reuse to achieve water self-sufficiency. This study evaluated the system's technical and economic viability. Weekly samples were taken pre- and post-treatment of both rain and greywater treatment and analysed for a set of water quality parameters. Treated greywater met reuse standards, and rainwater complied with most Swiss drinking water limits. However, occasional instances where limits were surpassed revealed the need for continuous monitoring and system adjustments. Throughout the 8-month monitoring period, the house achieved full water self-sufficiency, which utilized only 26% of collected rainwater and 24% of treated greywater, suggesting greater reuse potential. At this time, the house was not always fully occupied. A further dynamic simulation indicated that with full occupancy of up to three people, the house could maintain its water self-sufficiency. The energy consumption of the water treatment system was rather high due to the off-grid, water-self-sufficient design, which replaces centralized infrastructure. A cost analysis positioned the system as economically competitive when mandatory connection fees were excluded, highlighting the influence of regulatory frameworks on the adoption of such water systems.