Water pipes shall be laid a minimum of ______ above the sewer or drainpipe.

The minimum vertical distance that water pipes must be laid above sewer or drainpipes is typically defined to prevent contamination of the potable water supply. The correct answer reflects standard plumbing codes which specify that there should be sufficient separation to avoid any potential backflow or leakage that could cause harmful materials from the sewer to enter the drinking water supply. Maintaining this distance is crucial for ensuring public health and safety.

The other options provided do not meet the standard requirements, as they either specify measurements that are not aligned with plumbing codes or are insufficient to ensure the necessary safety margins. This highlights the importance of adhering to established guidelines in installation practices to prevent cross-contamination and uphold sanitation standards.