Final answer:
The maximum allowable pressure drop for a natural gas piping system is determined by local building codes or industry standards, and cannot be definitively answered without referencing the specific documents.
Step-by-step explanation:
The maximum pressure drop allowed by codes for a natural gas piping system with a supply pressure of a 7" water column is typically specified by local building codes or standards related to gas distribution. However, without the specific codes or standards referenced in the question, it is not possible to provide a definitive answer. It's essential to consult the relevant local building codes or industry standards to determine the allowed pressure drop for a particular installation.