Backflow protection is worked out by identifying each hazard on the premises and treating water as non-drinking going upstream from it until a device suitable for that hazard is reached. The drinking supply is protected by individual devices at each hazard, zone devices with identified downstream pipework, containment devices (including fire service devices), or a combination, each chosen from Table 4.4.1 for the hazard rating and for back-pressure or back-siphonage. AS 2845.2 governs registered air gaps and break tanks. Devices are chosen for the rating and table suitability (4.4.2), extra zone or individual devices are added wherever cross-connections are found (4.4.4), and heated water systems follow the same rules with devices suited to heated water (4.4.7).
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.