Bacteriostatic Water vs Sterile Water: What Is the Difference?
By the BacWaterPep editorial team · Updated
Short answer. Bacteriostatic water is sterile water with 0.9% benzyl alcohol added as a preservative, so a vial can be punctured repeatedly and is usually discarded 28 days after first use. Sterile water has no preservative: once opened it is for a single use.
| Preservative | Bacteriostatic: benzyl alcohol 0.9% (9 mg/mL) · Sterile: none |
|---|---|
| Vial type | Bacteriostatic: multi-dose · Sterile: single-use |
| After first puncture | Bacteriostatic: usually discard after 28 days · Sterile: discard after the one use |
| Typical sizes | Bacteriostatic: 3–30 mL · Sterile: 3–10 mL (larger for other uses) |
| Choose it when | Bacteriostatic: the vial will be re-entered · Sterile: benzyl alcohol must be avoided |
What the preservative does
Benzyl alcohol inhibits the growth of many bacteria introduced when a needle re-enters the vial. It does not sterilise a contaminated vial and has no effect on viruses, which is why opened vials still get a discard date (CDC).
Why the 28 days
Opened multi-dose vials are generally dated and discarded within 28 days unless the manufacturer specifies a different date (CDC). Single-dose vials such as sterile water are not re-entered at all.
When sterile water is the right choice
- Your method or compound documentation excludes benzyl alcohol.
- You use the whole vial at once.
- You are preparing material for neonatal-related research, where benzyl alcohol is a known hazard (see the benzyl alcohol article).
For buyers stocking both
Sellers who list both liquids reduce returns and questions: label them clearly as preserved / unpreserved, and keep sizes small for the single-use product.
Sources
- DailyMed — Bacteriostatic Water for Injection, USP (0.9% benzyl alcohol), Hospira label
- CDC — Preventing Unsafe Injection Practices (multi-dose vials, 28-day rule)
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