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What Is Water for Injection (WFI)?
The Definition of WFI
Water for Injection (WFI) is defined by the United States Pharmacopeia (USP) as purified water that meets additional requirements for endotoxin control, conductivity, and total organic carbon (TOC). It is the starting material for manufacturing all injectable pharmaceutical products, including bacteriostatic water, sterile water for injection, and many compounded sterile preparations.
How WFI Differs From Other Water Grades
| Water Type | Endotoxin Limit | Preservative | Primary Use |
|---|---|---|---|
| WFI | <0.25 EU/mL | None | Pharmaceutical manufacturing base |
| Bacteriostatic Water | <0.25 EU/mL | 0.9% Benzyl Alcohol | Multi-use research reconstitution |
| Sterile Water for Injection | <0.25 EU/mL | None | Single-use diluent/reconstitution |
| Purified Water (USP) | Not specified | None | Non-injectable pharmaceutical use |
| Deionized Water | Not controlled | None | Industrial/laboratory non-sterile use |
How Is WFI Produced?
Historically, WFI was produced exclusively by distillation — a process that separates water from impurities by evaporation and condensation. The USP now also permits membrane-based purification (reverse osmosis combined with ultrafiltration) for WFI production.
At Renew Lab Group, our bacteriostatic water starts from a WFI-quality water source, which is then combined with pharmaceutical-grade benzyl alcohol, sterile-filtered, and filled under cleanroom conditions. This is what makes the product truly pharmaceutical-grade — the quality of the starting water matters as much as the process.
WFI in Bacteriostatic Water Manufacturing
Bacteriostatic water is manufactured using WFI as the base. The production process involves:
- Starting with WFI-quality purified water
- Adding pharmaceutical-grade benzyl alcohol to 0.9% concentration
- Mixing under cleanroom conditions
- Sterile filtering through 0.22-micron membranes
- Filling into sterile vials under ISO Class 5 (or better) conditions
- Batch testing: HPLC, endotoxin, pH, sterility
Why Endotoxin Control Matters
Endotoxins are lipopolysaccharides (LPS) released from gram-negative bacterial cell walls. Even trace amounts (<1 EU/kg in intravenous use) can cause fever, inflammation, and septic shock in research subjects. WFI and all products derived from it must meet strict endotoxin limits — this is why LAL (Limulus Amebocyte Lysate) testing is mandatory for all injectable water products.
Learn more: Endotoxin Control in BAC Water Manufacturing | Understanding Your COA
Related Resources
Bacteriostatic Water vs Sterile Water | USP Manufacturing Standards | Shop BAC Water
