What Is Bacteriostatic Water?

Bacteriostatic water (BW) is sterile water for injection that contains 0.9% benzyl alcohol as a preservative. The benzyl alcohol inhibits bacterial growth — making it safe for multi-dose use over 28–30 days, unlike single-use sterile water.

Why Benzyl Alcohol Matters

Plain sterile water for injection carries no preservative. Once you pierce the septum, it is no longer sterile — microbial contamination can occur with each subsequent draw. Benzyl alcohol solves this: it maintains a bacteriostatic environment that prevents growth between doses.

The 0.9% concentration is the FDA-recognized standard for multi-dose injectable preparations. Higher concentrations are used in some pharmaceutical applications but are not appropriate for standard reconstitution work.

What It Is Not

• Not saline (0.9% sodium chloride solution)
• Not sterile water for injection (no preservative)
• Not distilled or filtered tap water
• Not for oral, topical, or veterinary use

Storage and Shelf Life

Unopened: store at room temperature, away from direct light. Shelf life is printed on the vial label. Once opened: refrigerate at 2–8°C (36–46°F). Discard 28–30 days after first puncture regardless of remaining volume. Do not freeze.

Multi-Dose Integrity

Each time you draw from a multi-dose vial, use a new syringe and needle and swab the septum with 70% isopropyl alcohol. Allow the swab area to air-dry 15 seconds before insertion. This maintains sterility between draws and is the main technique variable that determines how long the vial stays safe to use.