For how long must an air test on a water system be held and at what pressure?

An air test on a water system is a critical procedure used to ensure that the system is free from leaks and can maintain pressure. The requirement of holding an air test for a specified duration and at a specific pressure is designed to allow adequate time for any potential leaks to become apparent and to ensure that the system can tolerate the pressure without failure.

In this case, the correct answer specifies that the test should be conducted at a pressure of 700 kpa (100 psi) for a duration of 2 hours. This pressure level is high enough to test the integrity of the piping and fittings, ensuring that they can withstand typical operational pressures plus a safety margin. Additionally, the 2-hour duration allows sufficient time for visual inspection and for any minor leaks to be detected. It is important that these tests are conducted properly to maintain safety and reliability within plumbing systems.

The other options do not meet the combined criteria of pressure and duration set forth in plumbing codes or best practices. For example, conducting the test at a lower pressure may not thoroughly assess the system's integrity, while a different duration may not provide enough time to uncover leaks effectively.