Last updated: March 2026
Bacteriostatic water (BW) is sterile water containing 0.9% benzyl alcohol — the standard solvent for reconstituting lyophilized (freeze-dried) peptides. Unlike plain sterile water, BW is safe to re-enter multiple times over 28 days without bacterial contamination risk.
These two products look identical but serve fundamentally different purposes. Using the wrong one is a common and costly mistake in peptide protocols.
Benzyl alcohol (0.9%) is a bacteriostatic agent — it inhibits bacterial cell division without sterilizing the vial. Once you needle into the vial, skin bacteria can be introduced. The BnOH prevents those bacteria from multiplying to dangerous levels between uses. This is why BW is safe for multi-dose use; plain sterile water is not.
Lyophilized peptides are freeze-dried powders — highly stable for storage, but they must be reconstituted before injection. BW is the gold-standard solvent because: (1) it's sterile, (2) it's compatible with peptide chemistry at physiological pH, and (3) the preservative allows multi-dose use over weeks, matching most peptide protocols.
For a 5mg peptide vial + 1mL BW: concentration = 5mg/mL = 5000mcg/mL. On a U-100 insulin syringe, 1 unit = 0.01mL = 50mcg. For a 250mcg dose, draw to the 5-unit mark. Adding 2mL doubles the volume and halves the concentration. Use our calculator to get exact marks for any protocol.
Unopened BW vials: 2–3 years at room temperature. After first use: 28-day limit, refrigerate between uses (2–8°C recommended). Once reconstituted in BW, peptides themselves typically last 3–4 weeks refrigerated or 6+ months frozen. Discard if you see particulate matter, cloudiness, or color change.
Step-by-step safety criteria for handling bacteriostatic water and reconstituted peptides.
Everything you need for safe peptide reconstitution and injection.
Dosing schedules, interaction warnings, and cycle protocols for 50+ compounds — all in one place.
This page is for educational purposes only. It does not constitute medical advice. Bacteriostatic water and injectable compounds should only be used under the supervision of a qualified healthcare provider. Improper injection technique carries serious infection risks. Always follow sterile technique guidelines.