CEW 2025 Study confirms safe use of treated circular water
Numerous international research studies have focused on risk assessments regarding the public health and safety aspects of using alternative circular water for non-potable applications. The recent independent risk assessment study by the Centre of Expertise Water Technology (CEW, 2025) evaluated the microbiological risks of using treated greywater and rainwater in the built environment. The study confirms that public health risks are negligible when appropriate treatment and system design are applied for non-potable uses.
The CEW assessment shows that circular water can be safely used for toilet flushing and outdoor/garden irrigation, and for laundry use, provided that:
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water is treated according to fit-for-purpose standards,
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drinking water and circular water networks are strictly separated, and
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systems are properly designed, monitored, operated, and maintained.
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International practice supports these findings. In the United States and other regions, the NSF/ANSI-350 standard is widely used for on-site treatment and reuse of greywater. Within Europe, the relevant standards are EN 16941-1 (rainwater), EN 16941-2 (greywater), and EN 1717 (backflow and cross-connection protection). These standards define water quality benchmarks, required treatment steps, and system safeguards to ensure hygienic separation between drinking water and circular water networks.
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The CEW study emphasizes several conditions for safeguarding public health:
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Appropriate treatment to reduce microbiological contamination to fit-for-purpose water quality levels.
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Clear labelling and physical separation between drinking water and circular water pipelines in accordance with EN 1717, NSF-350.
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Periodic inspection and maintenance to ensure stable, long-term treatment performance.
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In multi-dwelling or collective systems, the use of a secondary disinfection barrier (e.g., UV-C, ultrafiltration, or equivalent) can provide an additional safeguard.
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Digital monitoring and operational diagnostics can support safe decentralised system management.​
Based on current scientific evidence and operational experience, the use of treated circular water for these non-potable applications is both feasible and safe, when implemented in accordance with established standards and operational guidelines. This provides a robust and validated foundation for scaling circular water solutions in the built environment.