A water test on a building drain requires at least a _____ head of water.

The requirement for a water test on a building drain to have at least a 10-foot head of water is based on standard plumbing practices to ensure the drain system can handle potential flows and pressures without failure. A 10-foot head effectively simulates the hydraulic pressure that would occur under typical operational conditions, allowing for a thorough assessment of the drain's integrity.

This level of testing helps identify any leaks, blockages, or weaknesses in the system, ensuring that the plumbing installation meets safety and performance standards. Lower head pressure could result in inadequate testing and possibly miss important issues that could lead to system failures or health hazards. This makes the 10-foot requirement significant in validating the functionality and reliability of the drainage system.