Where the water supply falls short of AS/NZS 2243.3, an assessment must decide whether backflow prevention is needed; the guideline suggests weighing the hazards of the GMOs to be used, any cross-connections, devices or systems that could contaminate a supply linked directly or indirectly to the water service, and how likely a backflow event is. If prevention is needed, measures suited to the GMO risks must be put in place, and records of the assessment and of any measures must be kept and given to the Regulator on request. AS/NZS 3500.1 is cited for selecting and installing backflow devices. The guideline's notes add that an aquatic facility may draw water from more than one source (for example a dedicated aquarium supply and a municipal supply for wash-up and staff use); that cross-connection with the municipal system could happen through, for example, a hose used to clean out bunding or a floor-drain sump dropping into effluent water; and that a dedicated source, for example a storage tank used only inside the facility is unlikely to back-siphon and would not need a device, unless pump back-pressure could push water back into the tank hard enough to make it overflow, in which case protection would be needed.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.