2.3.5 Sampling for Performance Qualification/Verification2.3.5.1 PurposeThe purpose of PQ/verification is to document that the stated water quality is delivered from the water system during:1. Typical (nominal) use conditions2. Worst case use conditions (system limits)3. Special scenariosand that the water complies with the requirements for the grade of pharmaceutical water type specified.The period for the PQ depends on whether it applies to a completely new system or to modifications made to an existing system.2.3.5.2 Typical Use Conditions (Nominal)All PQs include a period of normal operation or simulated normal operation to demonstrate that the water quality during normal operation complies with the requirements for the actual specified pharmaceutical water quality. Normal operational usage ranges are defined with rationales.2.3.5.3 Worst Case Use ConditionsA worst case scenario tests the limits of the system and is defined as the most extreme situations during the operation of the water system.Below are a few examples of worst case conditions: