Every water supply system must be designed, installed and maintained so contaminants cannot enter the drinking water supply. Nothing that could contaminate the supply may be joined to the water service, directly or indirectly, without cross-connection or backflow control suited to the hazard. A tank holding both drinking and other water needs a double partition with the space between drained visibly to the outside so a leak cannot pass between compartments. Connecting one water source to another (drinking to non-drinking, or between non-drinking supplies) requires backflow prevention. Backflow protection built into a fixture or appliance and suited to its hazard means no extra device is needed upstream; any cross-connection discovered should be notified to the water utility (Australia) or territorial authority (New Zealand).
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.