Water is one of the most essential raw materials in pharmaceutical manufacturing and analytical testing — but not all water is the same!
Let’s break down the three main grades commonly used in labs and manufacturing
Milli-Q Water
Definition:
Milli-Q water is ultrapure laboratory-grade water obtained through advanced purification (Millipore’s Milli-Q system) involving ion exchange, reverse osmosis, and 0.22 µm filtration.
Use:
While not officially defined in pharmacopeias (USP/BP), it is widely used for analytical applications such as:
🔹 HPLC
🔹 UV spectrophotometry
🔹 Preparation of analytical reagents
Typical Quality Parameters:
Resistivity ≥ 18.2 MΩ·cm @ 25°C
TOC ≤ 5 ppb
Bacteria < 1 CFU/mL
Endotoxin < 0.001 EU/mL
Note: Milli-Q water is not a pharmacopeial grade — it’s purely for laboratory analytical use.
Purified Water (PW)
Definition (USP & BP Monograph):
Produced by purification of potable water using processes like ion exchange, reverse osmosis, distillation, or electrodialysis.
Use:
✅ Non-sterile product manufacturing
✅ Equipment cleaning
✅ Feed water for Water for Injection (WFI) systems
Quality Parameters:
Conductivity ≤ 1.3 µS/cm @ 25°C
TOC ≤ 500 ppb
Microbial Limit ≤ 100 CFU/mL
Nitrates ≤ 0.2 ppm
Chloride ≤ 0.02%
Heavy Metals ≤ 0.0001%
Storage & Distribution:
Maintained in 316L stainless steel loops, typically at >70°C or under UV sterilization to prevent microbial growth.
Water for Injection (WFI)
Definition (USP <1231> & BP):
Highly purified water prepared by distillation or double-pass reverse osmosis with ultrafiltration, meeting stringent endotoxin and microbial limits.
Use:
💉 Parenteral (injectable) and sterile product manufacturing
🧴 Final rinsing of equipment in aseptic areas
Quality Parameters:
Conductivity ≤ 1.3 µS/cm @ 25°C
TOC ≤ 500 ppb
Endotoxin ≤ 0.25 EU/mL
Microbial Limit ≤ 10 CFU/100 mL
Production:
USP: Distillation or equivalent process
BP: Distillation only (for bulk WFI)
Storage & Distribution:
Kept at ≥ 80°C or 2–8°C with continuous circulation and microbial control.
Container WFI:
(For WFI in vials or ampoules) — must be sterile, pyrogen-free, and chemically equivalent to bulk WFI.
In summary:
Each water type serves a distinct purpose — from ultrapure Milli-Q water for analysis, to Purified Water for manufacturing, and WFI for sterile preparations.
Understanding their specifications ensures compliance, accuracy, and product safety across the pharma value chain.