WFI = Water for Injection
, WFI is ultra-pure water specifically produced to be used in the human body through injections.
It must be:
• Free from any microbes
• Completely free from endotoxins
• Free from organic substances that could react with drugs or the body
Uses of WFI:
• Preparing intravenous (IV) or intramuscular (IM) injections
• Cleaning sterilized production equipment
• Preparing sterile drugs or ophthalmic products
• Producing clean steam (for sterilization) • Sometimes used in CIP lines or for preparing certain APIs
How WFI is produced:
Two main methods:
1. Thermal distillation – the traditional, reliable, and most widely used method
2. Membrane systems (RO + UF) – require stricter control and monitoring, less common globally
Most pharmaceutical plants use a Multi-Effect Distiller (MED).
How MED works:
MED works in stages (effects):
1. Feed water (PW or Soft Water) enters the first stage and is heated with plant steam until it boils
2. The pure steam generated is used to heat the next stage
3. Each stage produces more steam, which is condensed at the end to provide ready-to-use WFI
Typical design: 3–7 stages for better energy efficiency and lower steam consumption
Components of each stage:
• Evaporator: to vaporize water and separate impurities
• Separator: to remove droplets or carryover impurities
• Condenser: to convert pure steam back into water
Common operating mistakes and their impact:
1. Unstable feed steam pressure
• reduces distillation efficiency and may fail to remove microbes or endotoxins
2. Ignoring separator check
• tiny droplets may carry impurities into WFI
3. Operating above designed flow rate
• reduces residence time and distillation effectiveness
4. Using a standard condenser without DTS
• risk of contaminated water entering WFI line
5. Running without an effective steam trap
• condensate buildup reduces heat transfer efficiency
6. Skipping periodic sensor calibration (Pressure/Temp/Level)
• false readings may hide operational issues