Bacteriostatic Water Guide
Bacteriostatic water is the gold standard for peptide reconstitution. Understanding its properties, proper use, and storage is essential for protecting your research materials and ensuring reliable experimental results.
Bacteriostatic water (BAC water) is sterile water containing 0.9% benzyl alcohol as a bacteriostatic preservative. This simple addition makes a significant difference in peptide research—extending the usable life of reconstituted peptides and reducing contamination risk.
What is Bacteriostatic Water?
Composition
| Base | Sterile Water for Injection (USP) |
| Preservative | 0.9% Benzyl Alcohol |
| pH | 5.0-7.0 |
| Osmolality | ~0 mOsm/kg (hypotonic) |
Key Properties
- Inhibits bacterial/fungal growth
- Multi-use vial compatible
- 28-day post-opening shelf life
- Compatible with most peptides
How Benzyl Alcohol Works
Benzyl alcohol disrupts bacterial cell membranes, preventing microorganisms from multiplying. At 0.9%, it's effective as a bacteriostatic agent (stops growth) but is not bactericidal (doesn't kill existing bacteria). This is why starting with sterile technique is still important.
Bacteriostatic Water vs. Sterile Water
| Property | Bacteriostatic Water | Sterile Water |
|---|---|---|
| Preservative | 0.9% Benzyl Alcohol | None |
| Multi-Dose Use | ✓ Yes (28 days) | ✗ No (single-use only) |
| Bacterial Growth Risk | Low | High after opening |
| Peptide Storage | Ideal for 2-4 weeks | Immediate use only |
| Cost Efficiency | Higher (reusable) | Lower per vial, but wasteful |
When to Use Sterile Water
Sterile water (without preservatives) is sometimes preferred for:
- • Single-use preparations discarded immediately after use
- • Certain sensitive peptides that may interact with benzyl alcohol
- • Research requiring preservative-free conditions
Proper Use Guidelines
1. Storage Before Opening
Store unopened vials at room temperature (20-25°C), protected from light. Refrigeration is acceptable but not required for sealed vials. Check expiration date before use.
2. First Use
Clean the rubber stopper with an alcohol swab before each use. Use a fresh, sterile needle each time you withdraw from the vial. Write the opening date on the vial for tracking.
3. After Opening
Refrigerate at 2-8°C after first puncture. Use within 28 days. Discard if the solution becomes cloudy, discolored, or contains visible particles.
4. Reconstitution Volume
Use enough BAC water to achieve your desired concentration. Common volumes are 1-2 mL per vial. Add slowly down the vial wall, not directly onto the peptide powder.
Shelf Life & Storage
Unopened
- • Shelf life: 2+ years from manufacture
- • Storage: Room temperature (20-25°C)
- • Light protection: Recommended
- • Check: Expiration date on vial
After Opening
- • Shelf life: 28 days maximum
- • Storage: Refrigerated (2-8°C)
- • Mark opening date on vial
- • Discard if any contamination signs
Frequently Asked Questions
What is bacteriostatic water?
Sterile water containing 0.9% benzyl alcohol as a preservative. The benzyl alcohol inhibits bacterial growth, allowing multi-dose use.
Why not use regular sterile water?
Sterile water has no preservatives and becomes contaminated quickly after opening. BAC water remains safe for 28 days when stored properly.
How long does BAC water last?
Unopened: 2+ years. After opening: 28 days when refrigerated. Always mark the opening date on the vial.
Can I use BAC water for all peptides?
Most research peptides work well with BAC water. Some require specific solvents—always check the peptide's documentation.
Where should I store BAC water?
Unopened: room temperature, protected from light. Opened: refrigerated at 2-8°C.
Related Guides
Complete Reconstitution Guide
Step-by-step peptide preparation
Reconstitution Mistakes
Common errors to avoid