A freeze-dried peptide is a powder. To be handled in the laboratory, it must be put back into solution, and the liquid used for this is not a detail: it is this which determines the sterility of the preparation and its shelf life. This is the role of bacteriostatic water.
What it contains
Bacteriostatic water is sterile water to which we add 0.9% benzyl alcohol. This alcohol is a bacteriostatic agent: it does not eliminate the microorganisms already present, but it prevents their multiplication. The nuance is important — the bottle is not sterilizing, it preserves an already acquired sterility.
This is precisely what makes it possible to draw several times from the same bottle without contaminating it, where preservative-free water becomes a culture medium from the first opening.
Bacteriostatic water or sterile water?
| Bacteriostatic water | Sterile water (PPI) | |
|---|---|---|
| Composition | Water + benzyl alcohol 0.9% | Purified water, without additives |
| Draws | Several | One only |
| After opening | 28 days in the refrigerator | Discard immediately |
| Everyday use | Multi-dose vials | Single preparation |
For a lyophilized powder intended for several successive draws, bacteriostatic water is used. Sterile water without preservatives only makes sense if all of it is consumed at once.
Conservation rules
Before opening, the bottle should be kept at room temperature, away from direct light. No need to refrigerate it.
After the first draw, the accepted reference is 28 days in the refrigerator, between 2 and 8°C. This duration is not an excessive precaution: it corresponds to the period during which the preservative remains effective. After this time, the bottle is thrown away, even half full. Write down the date of the first draw directly on the label, it's the easiest way to avoid making a mistake.
The rubber stopper is disinfected before each draw. A reconstituted vial can be stored in the refrigerator and handled without vigorous shaking: the peptides do not tolerate mechanical shock well. The subject is developed in our guide on storage of lyophilized peptides.
The most common errors
- Use distilled or mineral water : neither is sterile.
- Keep an opened bottle beyond 28 days : the preservative does not protect indefinitely.
- Project the liquid directly onto the powder : it is poured slowly along the wall of the bottle.
- Shake to speed up dissolution : the powder dissolves on its own, in a few minutes.
- Freezing a reconstituted solution : freezing cycles degrade most peptides.
What we provide
Our bottles of bacteriostatic water make 3 mL. A kit (water + 10 syringes + 10 pads) is free for each vial from €99.99. Below, the same material is checked directly on the form. The details are in the guide reconstitution equipment.
Reminder: our products are intended exclusively for laboratory research. We do not provide any protocols for use in humans or animals.
Fact sheet
- Composition
- Water for injections with 0.9% benzyl alcohol
- Role of benzyl alcohol
- Limiting bacterial growth in a vial punctured several times
- After opening
- Up to 28 days for a multi-dose vial, according to the USP 797 standard
- Difference from sterile water
- Sterile water contains no preservative: an opened vial is for single use only
- Known precaution
- Benzyl alcohol is contraindicated in newborns
What the research says
Summary of published data, written by the PeptidLab team. It describes molecules studied in the laboratory or in clinical trials: nothing here is an indication for use.
1982Human studyN Engl J Med
Description of "gasping syndrome" in newborns exposed to large amounts of benzyl alcohol: this is the origin of the neonatal contraindication.
Sources
Links to PubMed or to the original document. Articles in English.
- Gershanik J et al. The gasping syndrome and benzyl alcohol poisoning. N Engl J Med, 1982. PubMed
Updated October 2026.
Frequently asked questions
What is bacteriostatic water?
Sterile water with 0.9% benzyl alcohol, a preservative that prevents bacteria from multiplying. This is what allows you to draw several times from the same bottle.
What is the difference with sterile water for injections?
Sterile water does not contain any preservatives: it is intended for single use and must be thrown away after opening. Bacteriostatic water is preserved after the first draw.
How long does an opened bottle last?
The rule used by manufacturers is 28 days after the first draw, stored in the refrigerator. Beyond that, the bottle is thrown away, even if there is some left.
Can you use distilled water or tap water?
No. Neither is sterile: they contaminate the preparation and degrade the peptide. Only sterile water designed for this use is suitable.
Is bacteriostatic water supplied with the vials?
The kit (3 mL bacteriostatic water + 10 syringes + 10 swabs) is free with each vial starting at €99.99. Below, the water and the lot are checked on the product sheet.
This guide has an informative and scientific purpose. PeptidLab products are intended exclusively for laboratory research and are not intended for human or animal consumption.
