Bacteriostatic Water for Peptides

What is bacteriostatic water?

Bacteriostatic water (often shortened to BAC water) is sterile, non-pyrogenic water that contains 0.9% benzyl alcohol added as a preservative. That added benzyl alcohol is the single defining feature that separates it from plain sterile water. The preservative inhibits bacterial growth inside the vial, which is why a vial can be punctured and drawn from repeatedly over several weeks without microbial contamination of the solution. In a research setting it is the established standard vehicle for reconstituting lyophilised (freeze-dried) peptides.

Lyophilised peptides arrive as a dry powder cake and must be dissolved into a liquid before they can be handled, measured or studied in solution. The liquid used to do this is called the diluent or reconstitution vehicle. Bacteriostatic water is the most commonly chosen diluent for research peptide work because its preservative keeps the resulting solution stable and uncontaminated across the multi-week timeframe that most research protocols run over.

Why benzyl alcohol matters

Benzyl alcohol at 0.9% is a bacteriostatic agent. Bacteriostatic means it inhibits and prevents the growth and multiplication of bacteria rather than actively killing them. It is not bactericidal. It works by disrupting the integrity of the bacterial cell membrane, which stops bacteria from proliferating inside the vial. This is the mechanism that allows a single vial to be drawn from multiple times across a research protocol while the solution stays usable.

At the 0.9% concentration, benzyl alcohol is compatible with the vast majority of research peptide sequences. It does not denature peptide bonds and does not precipitate most peptides out of solution, which is why it became the default research diluent. The preservative is the reason a reconstituted vial keeps for a meaningful window rather than expiring almost immediately.

Bacteriostatic water vs sterile water vs saline

The three liquids most often compared as peptide diluents are bacteriostatic water, sterile water and 0.9% sodium chloride (saline). They look identical, but they behave very differently once a vial is opened. The key variable is whether a preservative is present, because that determines how long a reconstituted solution stays viable.

Sterile water is purified, sterilised water with no preservative. Once it is opened it can no longer guarantee protection against bacterial contamination, so a vial reconstituted with sterile water has only a short viable window, commonly cited as roughly 24 hours refrigerated, and is treated as single use. Saline is 0.9% sodium chloride in sterile water, again with no bacteriostatic preservative. It can dissolve peptides, but it offers no antimicrobial protection, and its salt content can potentially influence the stability of some peptide sequences. Bacteriostatic water is the option that supports multiple draws from one vial, which is why it suits multi-week research protocols.

Shelf life, storage and handling

Sealed, unopened bacteriostatic water typically carries a shelf life of roughly 2 to 3 years from manufacture, though this varies by manufacturer and the printed expiry date on the specific vial is always the authoritative figure. Store unopened vials at room temperature, around 15 to 30 degrees C, away from light, heat and moisture.

• Once opened or used to reconstitute a peptide, bacteriostatic water and the resulting solution commonly remain viable for up to around 28 days when stored refrigerated at 2 to 8 degrees C. This is a general guideline, not a guarantee, and stability varies considerably by peptide sequence.
• Warm room temperature can accelerate benzyl alcohol evaporation, which reduces preservative effectiveness and can shorten the viable window. Refrigeration after reconstitution is the standard handling recommendation.
• Lyophilised (dry) peptide stored frozen at around -20 degrees C generally remains stable for 2 or more years. A reconstituted solution should not be frozen.
• The 28 day and 24 hour figures are commonly cited general guidelines rather than lab-certified constants, so treat them as direction rather than hard limits and let the specific compound guide handling.

Standard lab practice when reconstituting is to add the diluent slowly down the inside glass wall of the vial rather than directing it straight onto the powder cake, then to swirl the vial gently in a circular motion until the powder dissolves. Vials are not shaken, because mechanical and shear stress and the foaming it causes can degrade peptide chains and reduce activity. These are general research handling principles, not a how-to-mix or how-to-inject protocol, and no specific volumes or concentrations are recommended here.

The Australian regulatory picture

This section is general information, not legal advice. Bacteriostatic water itself has not been evaluated or approved by the TGA for human use, and Australian suppliers provide it for research use only. Separately, most therapeutic research peptides, including compounds such as BPC-157, TB-500, CJC-1295 and Ipamorelin, are Schedule 4 (prescription only) under the Poisons Standard and are not approved by the TGA for human therapeutic use.

A TGA safety alert in April 2026 reiterated that unapproved substances such as BPC-157 and TB-500 are not for human use. Reporting also indicates that the TGA tightened peptide import enforcement during 2026, with greater attention to declarations of intended use. The precise procedural details of those import rules are still evolving, so we describe the general direction rather than stating specific thresholds as confirmed fact. For anything specific to your circumstances, consult the current TGA guidance directly.

Bacteriostatic water in every NovaPeptides kit

NovaPeptides includes bacteriostatic water in every complete research kit, so the correct diluent is on hand alongside the lyophilised peptide rather than being sourced separately. Each kit also ships with a Janoshik certificate of analysis (third-party lab testing) and Australian shipping, so the research handling described on this page is supported out of the box.

We position the included BAC water as a convenience and completeness point, not a sales pitch. There are no prices or cart on this site. If you want to confirm what a complete kit contains, or check which diluent suits a particular peptide sequence, enquiries are handled via WhatsApp through the NovaPeptides Research Team.

Frequently asked questions