What is Bacteriostatic (BAC) Water?
An overview of what BAC water is, how it's different from plain sterile water, and why it's the standard diluent for research peptides.
Definition
Bacteriostatic water is sterile water containing 0.9% benzyl alcohol, added specifically to inhibit the growth of bacteria within the solution. This is what distinguishes it from plain sterile water for injection (SWFI), which contains no such preservative.
BAC water vs. sterile water
| Bacteriostatic Water | Sterile Water (SWFI) |
|---|---|
| Contains 0.9% benzyl alcohol as a preservative | No preservative |
| Can typically be used across multiple draws over time | Generally intended for single-use only |
| Standard choice for reconstituting research peptides | Used where benzyl alcohol sensitivity is a concern |
Why it's used for peptide reconstitution
Freeze-dried (lyophilized) research peptides are shipped as a stable powder. Before use, they need to be dissolved in a liquid diluent. Because BAC water's preservative allows a reconstituted vial to remain viable for longer than plain sterile water would, it's the standard choice in laboratory settings where a vial may be accessed multiple times over several days or weeks.
Storage
Unopened BAC water vials are typically stored at room temperature. Once a peptide vial has been reconstituted using it, the resulting solution is generally kept refrigerated.