What is bacteriostatic water?
Bacteriostatic water explained: 0.9% benzyl alcohol, how it differs from sterile water, compatibility and how to handle multi-use vials in the lab.
Bacteriostatic water is sterile water that contains 0.9% benzyl alcohol (9 mg per ml). In the lab it is used as a diluent for reconstituting lyophilised peptides and other reagents, particularly when the same vial will be accessed more than once.
What “bacteriostatic” means
A bacteriostatic agent stops bacteria from multiplying; it does not reliably kill them. The benzyl alcohol in bacteriostatic water keeps the solution from becoming a growth medium if microorganisms are introduced when a needle passes through the stopper. That is why it is supplied in multi-use vials.
Bacteriostatic water vs sterile water
| Bacteriostatic water | Sterile water | |
|---|---|---|
| Contents | Water with 0.9% benzyl alcohol | Water only |
| Vial use | Multiple withdrawals | Single use; discard after opening |
| Shelf life once opened | Commonly 28 days | Use immediately |
| Compatibility | Not suitable for every compound | Neutral for most compounds |
Compatibility
Benzyl alcohol is a mild organic solvent and preservative. Most peptides reconstitute well in it, but some proteins and assays are sensitive to it. Check the literature for your compound and assay before choosing a diluent. If benzyl alcohol could interfere, use sterile water or a suitable buffer and treat the solution as single-use.
Handling and storage
- Store unopened vials at room temperature (about 20–25 °C), away from direct light.
- Wipe the stopper with 70% isopropyl alcohol before each puncture and let it dry.
- Label the vial with the date of first use and discard it after 28 days, or sooner if it becomes cloudy or shows particles.
- When reconstituting a peptide, run the liquid gently down the side of the vial and swirl rather than shake, to avoid foaming and aggregation.
Our bacteriostatic water
Peptide Pro bacteriostatic water is supplied in a sealed 10 ml multi-use vial. See also our guide to storing reconstituted peptides.
Peptide Pro bacteriostatic water is supplied for laboratory use only. It is not for human or veterinary use.