What Is Bacteriostatic Water
BAC water is not plain water. It contains exactly 0.9% benzyl alcohol (9 mg/mL) in sterile water for injection, presented in multi-dose vials sealed with a rubber septum.
Why Benzyl Alcohol
Benzyl alcohol is an antimicrobial preservative that inhibits the growth of bacteria, mold, and fungi at the 0.9% concentration. This bacteriostatic (not bactericidal) action prevents contamination of the vial during repeated needle insertions over 28-30 days. Without it, each needle puncture introduces risk of contamination.[1]Multi-Dose Use
The benzyl alcohol preservative makes BAC water safe for multi-dose use, a single 30 mL vial can serve as the diluent for an entire reconstitution session and be accessed repeatedly over the following weeks. Plain sterile water, saline, or water for injection do not contain preservatives and should only be used for single-dose reconstitution.BAC Water vs. Alternatives
Choosing the wrong diluent is one of the most common reconstitution mistakes.
BAC Water (Recommended for Most Peptides)
Use for: virtually all lyophilized" class="wiki-gloss-link">lyophilized research peptides. Multi-dose vials over 28-30 days. Any peptide that will be stored refrigerated and used over weeks.Sterile Water for Injection (Single Use)
Use for: single-dose reconstitution when the entire vial will be used immediately. Peptides sensitive to benzyl alcohol (very rare; check specific peptide data). No preservative, do not store for multi-dose use.Normal Saline (0.9% NaCl)
Generally avoided for peptide reconstitution, the sodium chloride can destabilize some peptides and affect pH. Reserved for clinical IV dilution applications.Acetic Acid Solution (0.1%, 1%)
Required for select peptides that are insoluble in neutral pH water. IGF-1, Follistatin, and some growth factors require slight acid pH for solubility. Check peptide-specific reconstitution guidance.Calculate your Bacteriostatic Water dose Vial strength, BAC water, exact syringe draw in IU. Free, no signup. Open Calc →
Shelf Life and Storage
Reconstituted Peptide Shelf Life with BAC Water
Most research peptides reconstituted in BAC water remain stable for 28-30 days when stored at 2-8°C (refrigerated). This assumes:- Clean reconstitution technique (new needle, new syringe for each injection) - Storage in opaque or foil-wrapped vial (protect from light) - Vial kept refrigerated between uses, never left at room temperature for extended periods
BAC Water Vial Shelf Life
Unopened BAC water vials are stable at room temperature per manufacturer specification. Once opened, use within 28 days, storing at room temperature or refrigerated per label.Signs of Degraded Peptide Solution
Discard if the reconstituted solution: appears cloudy or turbid (should be clear), has visible particulate matter, has changed color, or smells unusual. When in doubt, discard and reconstitute fresh.Benzyl Alcohol Safety
Adult use: 0.9% benzyl alcohol is safe for adult subcutaneous injection. The total benzyl alcohol dose per typical peptide injection (0.1-0.5 mL BAC water) is 0.9-4.5 mg, well below any toxic threshold.
Neonatal contraindication: Benzyl alcohol is contraindicated in neonates (newborns). "Gasping syndrome", a potentially fatal metabolic acidosis - has been associated with large-volume IV benzyl alcohol in neonates. Not relevant for adult SC peptide protocols.
Benzyl alcohol sensitivity: Rare benzyl alcohol hypersensitivity exists. Injection site redness beyond normal is a warning sign. If suspected, switch to sterile water for injection (single-dose).
Obtaining BAC Water
BAC water is widely available without prescription in most jurisdictions.
Pharmacy / compounding pharmacy: Standard 30 mL multi-dose vials are available from pharmacies as USP-grade water for injection. Ask specifically for "bacteriostatic water for injection 0.9% benzyl alcohol."
Online suppliers: Research chemical and peptide suppliers typically include BAC water with orders or sell it separately. Ensure it is labeled "for injection", not just "bacteriostatic water."
Volume: 30 mL vials are standard and cost-effective for reconstituting multiple peptide vials. 10 mL vials are also available.
References
- [1]United States Pharmacopeia (USP). "Water for Injection." USP 40-NF 35. General Chapter <1>.
- [2]FDA. "Benzyl Alcohol Toxicity in Neonates." Drug Safety Communications. 1982.