What is required for a plumbing system to comply with cross-connection control?

For a plumbing system to comply with cross-connection control, the necessity of backflow prevention devices for all fixtures is paramount. Cross-connections can occur when there is a direct connection between the potable water supply and any non-potable source, which presents a risk for contaminants to enter the drinking water system.

Backflow prevention devices serve as barriers that protect the potable water supply from potential contaminated water being siphoned back into the system. These devices ensure that water flows in one direction and prevents backflow, which is crucial for maintaining public health and safety standards.

The other options, while they may have roles in a plumbing system, do not directly address the critical need for controlling cross-connections. For instance, a constant flow of water doesn't eliminate the risk of contamination; color-coded plumbing materials can help identify pipes but do not prevent backflow; and regular pressure testing may ensure system integrity but is not a substitute for actual prevention mechanisms like backflow devices. Hence, the use of backflow prevention devices is the most effective and necessary measure for compliance with cross-connection control.