Air pressure equivalent to a _____ inch water column is required for a final air test on the drainage system.

For a final air test on the drainage system, an air pressure equivalent to a 1-inch water column is specified. This measurement is based on standard plumbing testing protocols that ensure the integrity of the drainage system by checking for leaks.

Using a 1-inch water column provides a consistent and manageable pressure that is sufficient to identify any potential weaknesses or leaks in the system without subjecting it to excessive stress. If the pressure were lower, such as 0.5 inches, it might not accurately reveal minor leaks; conversely, a higher pressure like 2 or 3 inches could unnecessarily complicate the testing process and risk damaging the system.

Thus, the use of a 1-inch water column is a balance that ensures reliability and safety in confirming the system's airtight integrity prior to its operation.