What Is Bacteriostatic Water?
Bacteriostatic water is the standard diluent used to reconstitute lyophilized research peptides. It looks like ordinary water, but one small addition — a preservative — makes it uniquely suited to laboratory work where a single vial is drawn from repeatedly over days or weeks. This guide explains what bacteriostatic water is, how it differs from the other kinds of water you'll encounter, and why it's the default choice for reconstitution.
The short definition
Bacteriostatic water is sterile water that contains 0.9% benzyl alcohol as a bacteriostatic preservative. "Bacteriostatic" means the additive holds bacterial growth in check — it doesn't sterilize on contact, but it prevents microbes from multiplying inside the vial. That single property is what lets a researcher withdraw from the same vial multiple times without the contents spoiling.
Plain sterile water is single-use — once you break the seal, there's nothing stopping contamination. The 0.9% benzyl alcohol in bacteriostatic water suppresses bacterial growth, so the vial stays usable across repeated withdrawals. That's the whole reason it's preferred for reconstituting peptides handled over time.
Bacteriostatic vs. other types of water
Not all water is interchangeable in the lab. The differences come down to what's been removed and what's been added.
| Type | What it is | Reuse |
|---|---|---|
| Bacteriostatic water | Sterile water + 0.9% benzyl alcohol | Multiple withdrawals |
| Sterile water for injection | Sterile, no preservative | Single use |
| Distilled water | Purified by distillation, not necessarily sterile | Not for reconstitution |
| Tap / spring water | Contains minerals and microbes | Never |
How it's used in reconstitution
Reconstitution is the process of dissolving a freeze-dried peptide back into liquid. Bacteriostatic water is added slowly to the vial — directed against the glass wall, not blasted onto the powder — and the peptide is left to dissolve with a gentle swirl rather than shaking. The preservative then keeps the resulting solution stable across the repeated withdrawals a research workflow involves. For the full method, see our guide on storing and reconstituting peptides.
Storage and shelf life
Sealed bacteriostatic water is stable at room temperature and has a long shelf life. Once opened, it should be kept clean, capped, and — like reconstituted peptide solutions — is best refrigerated and used within a reasonable window. Always inspect it before use: it should be clear and free of particulates.
- Keep it sealed until needed — an unopened vial stores easily at room temperature.
- Refrigerate after opening and use within the manufacturer's stated window.
- Inspect before use — discard anything cloudy or containing particles.
Bacteriostatic water is simply sterile water with a preservative that lets one vial be used many times. For reconstituting lyophilized research peptides, it's the standard diluent — reach for it over sterile-single-use, distilled, or any other water.
Bacteriostatic water, shipped from Canada
Sealed and research-grade, alongside our full catalog of third-party tested compounds.
Browse the CatalogReferences & Sources
Key statements in this article can be checked against the following independent sources:
- Bacteriostatic Water for Injection, USP (0.9% benzyl alcohol) — official product label, DailyMed / U.S. National Library of Medicine
- Manning MC et al. — "Stability of protein pharmaceuticals: an update," Pharmaceutical Research 27 (2010)
Compound-specific studies for the peptides sold on this site are listed, with their authors, in our Peer-Reviewed Research library. Provided for in-vitro laboratory and scientific research reference only — not for human consumption, and not medical advice.