Collecting rainwater for non-potable use — and keeping the wholesome supply protected.
Rainwater harvesting collects rain (usually from the roof) for non-potable uses such as WC flushing, the garden, or a washing machine — reducing mains water use.
The system. Roof → filter → storage tank → pump/feed to the non-potable outlets. Provide an adequately sized overflow to the suitable surface-water outfall. Protect the tank from drain backflow where the overflow connects to a drain or sewer.
The critical safety point. Harvested rainwater is not wholesome — it must never cross-connect with the mains supply. Mains backup needs fluid category 5 protection, commonly a correctly installed Type AA or AB air gap. Maintain the specified inlet clearance and overflow and prevent splash reaching the mains inlet. Mark non-potable pipes and outlets clearly so users and workers can recognise them; marking complements physical separation and cross-connection checks.
The water-fittings regulations/byelaws apply where there is a mains supply, including backup. Notify the water undertaker of proposed alternative-supply work. A washing machine must not cross-connect the non-potable supply with domestic wholesome hot/cold supplies. Greywater reuse follows the same separation principle, with treatment appropriate to its sources and intended uses.
Why filter before storage
Roof run-off carries leaves, moss, grit and bird droppings that wash off between showers. A first-flush diverter rejects an early portion of run-off, while a filter removes material according to its design. These can reduce what enters storage, but they do not guarantee drinking-water quality or remove the need to clean filters and maintain the tank. Dry-run protection stops a pump operating without enough water; mains backup is a separate supply provision whose performance depends on the layout. Neither replaces debris control.