What must be present in systems that use non-potable water for flushing?

In systems that utilize non-potable water for flushing, the presence of independent systems is essential for several reasons. Non-potable water generally contains contaminants that are not safe for human consumption. Therefore, having an independent system ensures that the plumbing for non-potable water is separate from the potable water supply. This separation is critical to prevent cross-contamination, which could pose serious health risks.

By establishing independent systems, regulatory standards and building codes are met, promoting safety and protecting public health. Utilizing separate piping and systems mitigates the risk of unintentional mixing, making sure that the potable water remains uncontaminated and safe for drinking and other uses.

Other options, while important in specific scenarios, do not address the fundamental requirement of keeping the systems separate to ensure safety and compliance with health regulations when dealing with non-potable water.