Bacteriostatic Water
Sterile diluent used to reconstitute lyophilized peptides in laboratory settings.
Also known as: Bac water, Bacteriostatic water for injection
Bacteriostatic water is sterile water containing 0.9 percent benzyl alcohol as a preservative. Unlike sterile water for injection, which is single-use, bacteriostatic water is designed for multiple withdrawals over a limited period. In research contexts it is commonly used as the reconstitution fluid for lyophilized peptides.
Key facts
- Composition
- Sterile water with 0.9 percent benzyl alcohol as bacteriostatic preservative
- Purpose
- Diluent for multi-dose reconstitution in pharmaceutical and research settings
- Typical packaging
- Sealed vials, commonly 10 mL, 20 mL, or 30 mL
- Shelf life after opening
- Typically labeled for use within 28 days of first puncture
- Not appropriate for
- Neonates (benzyl alcohol is contraindicated); large-volume infusions
What is bacteriostatic water?
Bacteriostatic water for injection is a pharmaceutical-grade preparation of sterile water that includes 0.9 percent benzyl alcohol. The benzyl alcohol serves as a bacteriostatic agent, meaning it inhibits the growth of most common bacteria that might be introduced when the vial stopper is punctured multiple times.
The product is manufactured by several pharmaceutical companies under USP monograph standards. It is distinct from sterile water for injection, which contains no preservative and is intended for single use, and from normal saline, which contains sodium chloride at physiologic concentration.
How it is used in research
Many research peptides are supplied as lyophilized (freeze-dried) powder in sealed vials. Before the peptide can be accurately measured or used in an experiment, it must be reconstituted by adding a liquid diluent. Bacteriostatic water is a common choice because it allows multiple small withdrawals from the same vial over time without rapid bacterial contamination.
Researchers typically calculate the reconstitution volume to achieve a target peptide concentration based on the labeled mass in the vial. After reconstitution, the peptide solution is usually stored refrigerated and used within the window specified by the product documentation.
Important limitations
Bacteriostatic water is not appropriate for use in neonates because benzyl alcohol has been associated with toxicity in newborns (sometimes referred to as gasping syndrome). This is a well-established contraindication in pharmaceutical use of benzyl alcohol-containing products.
Bacteriostatic water is also not appropriate for large-volume intravenous infusions, because the benzyl alcohol can accumulate to toxic levels at high doses. In clinical practice, it is used for reconstituting small-volume injectable drugs that will be administered in total volumes where the benzyl alcohol load remains within safe limits for adults.
Regulatory context
In the United States, bacteriostatic water is classified as a prescription product when distributed by pharmaceutical companies for clinical use. It is manufactured under FDA oversight and carries USP grade labeling. Research-grade bacteriostatic water sold for laboratory peptide reconstitution is distinct from the prescription clinical product and is intended for laboratory use only.
Research sourcing
Bacteriostatic Water is listed by our research partner, GLP1 Research Lab, which supplies lyophilized peptides for laboratory use. Listings include product identifiers relevant to research documentation.
View Bacteriostatic Water listing at GLP1 Research LabAffiliate partnership. Metabolic Playbook may earn a commission on purchases made through this link at no additional cost to the researcher.