A complete guide to bacteriostatic water — its composition, how it differs from sterile water and normal saline, and why it is the preferred solvent for reconstituting peptides in laboratory research.
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Bacteriostatic water (commonly called "BAC water") is sterile water that contains 0.9% benzyl alcohol as a bacteriostatic preservative. It is classified as a pharmaceutical-grade solvent and is widely used in laboratory settings to reconstitute lyophilized (freeze-dried) compounds, including research peptides.
The term "bacteriostatic" means "bacteria-inhibiting." Unlike plain sterile water, bacteriostatic water is specifically formulated to prevent the growth and reproduction of bacteria that might be introduced during repeated vial access. This preservative property makes it the standard solvent for multi-use research applications where a single vial may be accessed numerous times over days or weeks.
Bacteriostatic water is supplied in sealed, single-dose or multi-dose vials — most commonly in 10 mL and 30 mL sizes. It is a clear, colorless solution with a neutral pH, designed to dissolve lyophilized compounds without introducing ionic interference or altering peptide stability.
Bacteriostatic water is composed of two ingredients: USP-grade Water for Injection (WFI) and 0.9% (v/v) benzyl alcohol. The benzyl alcohol serves as the active preservative agent.
Benzyl alcohol (C6H5CH2OH) is a mild aromatic alcohol that functions as a bacteriostatic agent at the 0.9% concentration. Its mechanism of action involves disrupting microbial cell membrane integrity. When bacteria are introduced into the solution — for instance, through a needle puncture — benzyl alcohol interacts with the lipid bilayer of bacterial cell membranes, increasing membrane permeability and inhibiting cellular reproduction.
It is important to note that benzyl alcohol is bacteriostatic, not bacteriocidal. This means it inhibits bacterial growth and replication rather than actively killing existing organisms. The distinction is relevant: the preservative maintains a hostile environment for microbial proliferation but relies on aseptic technique during handling to minimize initial contamination.
At the 0.9% concentration used in bacteriostatic water, benzyl alcohol is effective against a broad spectrum of gram-positive and gram-negative bacteria while remaining compatible with most peptide compounds used in research.
Understanding the differences between bacteriostatic water and sterile water is essential for researchers selecting the appropriate solvent for their protocols.
| Property | Bacteriostatic Water | Sterile Water for Injection |
|---|---|---|
| Preservative | 0.9% benzyl alcohol | None |
| Multi-use | Yes (up to 28 days after opening) | No (single-use only) |
| Bacterial inhibition | Yes | No |
| Shelf life after puncture | Up to 28 days | Use immediately; discard remainder |
| Common research use | Peptide reconstitution, multi-dose protocols | Single-use dilutions, IV preparations |
Use bacteriostatic water when the reconstituted compound will be accessed multiple times over a period of days or weeks. This is the standard recommendation for most peptide reconstitution protocols in research.
Use sterile water when a preservative-free solution is specifically required by the experimental protocol, or when the entire reconstituted volume will be used in a single session with no remaining solution.
Normal saline (0.9% sodium chloride solution) is another common laboratory solvent, but it serves a different purpose than bacteriostatic water and is generally not recommended for peptide reconstitution.
While normal saline is isotonic and widely available, it introduces sodium and chloride ions into solution. These ions can interact with charged amino acid residues on peptide chains, potentially affecting peptide folding, solubility, or stability. Additionally, standard normal saline does not contain a preservative, making it unsuitable for multi-use access.
Bacteriostatic sodium chloride (0.9% NaCl with 0.9% benzyl alcohol) does exist but is used primarily in clinical contexts rather than peptide research. For reconstituting research peptides, plain bacteriostatic water remains the preferred choice because it provides a clean solvent environment free of ionic interference while still offering the preservative benefit.
Bacteriostatic water has become the standard reconstitution solvent for research peptides for several important reasons:
For these reasons, bacteriostatic water is the recommended solvent for reconstituting peptides such as BPC-157 and other research compounds available from reputable suppliers.
Correct handling and storage of bacteriostatic water are essential for maintaining its sterility and preservative effectiveness throughout its usable life.
Once bacteriostatic water has been used to reconstitute a peptide, the resulting solution should be stored according to the specific peptide's requirements — typically refrigerated at 2-8°C. For detailed guidance on post-reconstitution storage protocols, see our guide on how to store reconstituted peptides.
Reconstituting a lyophilized peptide with bacteriostatic water is a straightforward process, but proper technique is critical to preserving peptide integrity and avoiding contamination. The basic steps include:
For a comprehensive, step-by-step walkthrough — including volume calculations, concentration formulas, and troubleshooting tips — see our complete peptide reconstitution guide.
Not all bacteriostatic water is created equal. When sourcing BAC water for peptide research, researchers should verify that the product meets established quality standards:
Sourcing from a reputable vendor that provides transparent documentation and maintains strict quality controls is essential for reliable research outcomes. Browse our full catalog for USP-grade bacteriostatic water and research peptides.
Bacteriostatic water is used to reconstitute lyophilized (freeze-dried) peptides for laboratory research. The 0.9% benzyl alcohol preservative inhibits bacterial growth, allowing researchers to draw multiple doses from a single vial over an extended period without contamination. This makes it the preferred solvent for multi-use peptide reconstitution in research settings.
The key difference is that bacteriostatic water contains 0.9% benzyl alcohol as a bacteriostatic preservative, while sterile water contains no additives. Sterile water is intended for single-use applications only, as it has no mechanism to prevent microbial growth after opening. Bacteriostatic water allows multiple entries into the same vial over up to 28 days because the benzyl alcohol continuously inhibits bacterial proliferation.
Once punctured, bacteriostatic water is generally considered viable for up to 28 days when stored properly. Unopened vials retain stability until the manufacturer's printed expiration date. After opening, store the vial at controlled room temperature (20-25°C) or refrigerated (2-8°C), and always use aseptic technique when withdrawing solution to maintain sterility.
Unopened bacteriostatic water can be stored at controlled room temperature (20-25°C) away from direct light. After opening, refrigeration at 2-8°C is recommended by many researchers to further support stability, though room temperature storage remains acceptable within the 28-day use window. Always follow the manufacturer's specific storage instructions provided on the label.
Normal saline (0.9% sodium chloride) is not typically recommended as a substitute for bacteriostatic water in peptide reconstitution. While normal saline is isotonic, it lacks the benzyl alcohol preservative that inhibits bacterial growth. Some peptides may also be sensitive to the ionic strength introduced by the sodium chloride. Bacteriostatic water remains the standard solvent recommended for reconstituting research peptides.
Access USP-grade bacteriostatic water and research-grade peptides with full documentation for your laboratory investigations.
View Certificates of Analysis Browse Bacteriostatic WaterDisclaimer: All products referenced in this article are intended for laboratory research use only. They are not approved for human or veterinary use. Bacteriostatic water should be handled using aseptic technique in accordance with established laboratory protocols.