Bacteriostatic Water Explained: What It Is and How It Differs from Sterile Water
Bacteriostatic water is sterile water containing a small amount of benzyl alcohol, used as a diluent where a vial will be accessed more than once. This guide explains how it differs from sterile water.
Key takeaways
- Bacteriostatic water is sterile water with 0.9 percent benzyl alcohol added as a preservative.
- The preservative inhibits bacterial growth but does not sterilize a contaminated vial.
- Choose the diluent that suits your protocol; bacteriostatic and plain sterile water are not interchangeable.
What it is
Bacteriostatic water is sterile water that contains 0.9 percent benzyl alcohol. Benzyl alcohol is a preservative that inhibits the growth of bacteria, which is what “bacteriostatic” means. It differs from a bactericidal agent, which kills bacteria.
Bacteriostatic water versus sterile water
- Sterile water has no preservative. It is normally intended for single use, because once a vial is punctured there is nothing to slow bacterial growth.
- Bacteriostatic water includes benzyl alcohol so that a multi-dose vial can be accessed several times.
- Saline is a salt solution and is a different diluent altogether.
Why the choice matters in the laboratory
The right diluent depends on the compound and the protocol. Some experiments cannot tolerate a preservative such as benzyl alcohol, for instance certain cell-culture work, and would call for sterile water instead. Others benefit from a preserved diluent when the same vial is opened repeatedly.
Handling notes
- The preservative does not sterilize a contaminated vial, so aseptic technique is still required.
- Multi-use vials are commonly given a limited in-use period after first puncture; follow the manufacturer’s labelling.
- Record the date a vial was first opened.
Storage principles for peptides themselves are in our storage and handling guide. See the Bacteriostatic Water collection for available sizes. This guide is educational and not medical advice.