Off-grid water treatment and reuse of rain- and greywater on household level : pilot operation at the example of KREIS-Haus, Switzerland

The challenge of urban water scarcity, accentuated by climate change, calls for innovative solutions like KREIS-Haus – an inhabited living lab in Feldbach, Switzerland, demonstrating a decentralized, closed-loop water system. The aim of this study was to evaluate the technical and economic viability of KREIS-Haus's water system, integrating rainwater harvesting and greywater treatment and reuse within a single household setting to achieve water self-sufficiency. Weekly samples were taken pre- and post-treatment of both rain- and greywater treatment and analysed for a set of abiotic and microbial parameters. The effectiveness of the two treatment systems resulted in satisfactory removal rates for COD, BOD5, turbidity and microbial parameters in greywater, however moderate removal rates in rainwater treatment. The treated rain- and greywater was evaluated for its suitability in domestic applications, including drinking, showering, laundry, toilet flushing, and irrigation. The results indicated general adherence, although occasional exceedances highlighted the need for continuous monitoring and system adjustments. Throughout the experimental period, the house maintained complete water self-sufficiency, relying exclusively on rainwater without the need for external water sources. The study also examined the water system's energy usage, resulting in a greater consumption than global averages for wastewater treatment, but with room for improvement through optimization. A cost analysis positions the system as economically competitive, but only when the mandatory connection fees were excluded, thereby underscoring the influence of regulatory frameworks on the adoption of such water systems.