What Is Bacteriostatic Water?
Bacteriostatic water (BAC water) is sterile water containing 0.9% benzyl alcohol as a preservative. The benzyl alcohol inhibits bacterial growth, making the solution safe for multiple-use vials. This is the standard diluent for reconstituting lyophilized peptides.
It is dispensed in sealed, sterile vials (typically 10 mL or 30 mL) and must remain sterile throughout use.
BAC Water vs. Sterile Water vs. Saline
Bacteriostatic Water: Contains 0.9% benzyl alcohol preservative. Safe for multi-dose vials. The gold standard for peptide reconstitution. Shelf life: 28 days after first puncture.
Sterile Water for Injection: No preservative. Must be used within 24 hours of opening. Only appropriate for single-use vials. Slightly cheaper but far less practical.
Bacteriostatic Normal Saline (0.9% NaCl + 0.9% benzyl alcohol): Sometimes used as an alternative. The sodium chloride makes it isotonic, which may reduce injection site irritation. Suitable for peptides that are compatible with saline.
Recommendation: Always use BAC water unless you have a specific reason to choose otherwise.
How Much BAC Water to Add
The amount of water determines your solution concentration. Common reconstitution volumes:
• 5 mg vial + 1 mL = 5 mg/mL (concentrated — smaller injection volumes)
• 5 mg vial + 2 mL = 2.5 mg/mL (standard — easiest for most doses)
• 10 mg vial + 2 mL = 5 mg/mL
• 10 mg vial + 3 mL = 3.33 mg/mL
Use our Reconstitution Calculator or Reverse Calculator to find the optimal volume.
Storage and Handling
• Store unopened BAC water at room temperature (15-30°C), protected from light
• After first puncture, store at room temperature or refrigerate
• Discard 28 days after first opening
• Always swab the rubber stopper with alcohol before each use
• Use a new, sterile syringe each time you draw from the vial
Sourcing BAC Water
BAC water is widely available from pharmacies, medical supply companies, and online retailers. Look for:
• USP-grade (United States Pharmacopeia standard)
• Manufactured in FDA-registered facilities
• Clear packaging showing 0.9% benzyl alcohol concentration
• Reasonable pricing: typically $5-15 for a 30 mL vial