A copper water supply system is to be tested by means of air pressure. What MINIMUM pressure should be used

A pressure of 5 psi is far too low to effectively test the integrity of a copper water supply system. This minimal pressure would not provide sufficient force to identify leaks or weaknesses, as it is below the standard testing requirements for plumbing systems.

While 10 psi is higher than 5 psi, it is still inadequate for testing a copper water supply system. Similar to the previous choice, this pressure does not meet the necessary threshold to reliably assess the system's ability to withstand operational conditions and to ensure safety.

Using the working pressure of the system for testing is not appropriate as it does not provide a safety margin to identify leaks or issues. Testing is usually conducted at a level above normal operating pressures, and the minimum required testing pressure is specifically set at 50 psi to ensure thorough examination.