BS 8515:2009+A1:2013 Rainwater harvesting systems — Code of practice
About this book
BS 8515:2009+A1:2013, "Rainwater Harvesting Systems — Code of Practice," is a British Standard published by the British Standards Institution (BSI) that provides recommendations and guidance for the design, installation, testing, commissioning, and maintenance of rainwater harvesting systems for buildings. It is the primary technical standard in the UK for systems that collect roof rainfall, store it, and distribute it for non-potable uses such as toilet flushing, garden irrigation, and industrial processes. The standard defines the key components of a compliant rainwater harvesting system: the collection surface (typically a roof), the first-flush diverter (which discards the first portion of rainfall that carries the most contamination), the storage tank (sized according to rainfall data, roof area, demand, and overflow provision), the filter and treatment train, the pumped distribution system, and the backflow prevention and cross-connection controls that prevent contamination of the potable water supply.
Tank sizing is a critical design parameter addressed in detail. The standard provides methodologies based on the balance between supply (rainfall and roof area) and demand (intended end uses and occupancy), with the goal of maximizing yield while avoiding excessive dead storage. Guidance covers both manual calculation approaches and computer-based simulation methods, and references the Environment Agency's approved calculator for UK conditions.
Water quality requirements are specified for different end uses: the standard distinguishes between systems serving only toilet cisterns (where microbiological quality requirements are relatively low) and those also supplying laundry machines, garden irrigation, or vehicle washing (where higher treatment standards apply). Ultraviolet disinfection is typically required where direct human contact with the water is possible. A significant section addresses commissioning, testing, and handover, reflecting the importance of verifying that all components function correctly and that backflow prevention is effective before a system is put into operation.
The labelling requirements for pipework, storage tanks, and outlets are specified to prevent confusion with the potable water system. The UK Water Supply (Water Fittings) Regulations 1999 mandate certain design requirements for non-potable systems that BS 8515 addresses comprehensively, making compliance with the standard effectively mandatory for systems connected to buildings with mains water supply. Sources: British Standards Institution (bsigroup.com); BS 8515:2009+A1:2013 official publication; Environment Agency guidance on rainwater harvesting.