How to Design a GMP Purified Water (PW) System: Advanced Engineering & Validation Considerations

Designing a GMP purified water system requires more than selecting RO and EDI. It demands an integrated approach covering process robustness, hygienic design, microbial control, and lifecycle validation. The following guide reflects best practices aligned with USP, EP, WHO GMP, ISPE Baseline Guide, and FDA expectations.

1. Define Critical Quality Attributes (CQA) & Critical Process Parameters (CPP)

A compliant design starts with linking water quality targets (CQA) to controllable system variables (CPP).

Typical CQAs:

• Conductivity (≤ 1.3 µS/cm @25°C)
• TOC (≤ 500 ppb or project-specific)
• Microbial count (≤ 100 CFU/mL, often tighter internal limits)

Key CPPs:

• RO recovery and rejection rate
• EDI current density and feed conductivity
• Loop velocity and temperature
• Sanitization parameters (time, temperature, ozone concentration)