Bacteriostatic water (BAC water) is sterile water that contains 0.9% benzyl alcohol as a preservative. It is the standard solvent for reconstituting lyophilized (freeze-dried) peptides in research settings — and understanding why it’s preferred over alternatives is fundamental to maintaining peptide integrity and experimental reproducibility.
Why Bacteriostatic Water for Peptides?
The benzyl alcohol in BAC water serves a critical function: it inhibits bacterial growth in the reconstituted solution. Once a lyophilized peptide is dissolved in liquid, it becomes a nutrient-containing solution at a temperature range favorable for microbial growth. Without an antimicrobial preservative, bacteria can colonize the solution within hours to days, compromising both the peptide and any experimental results derived from it.
This preservative action is what gives BAC water its approximately 28-day usable life after first puncture — significantly longer than sterile water, which offers no antimicrobial protection and should be used within 24 hours.
Bacteriostatic Water vs. Sterile Water vs. Normal Saline
| Property | Bacteriostatic Water | Sterile Water | Normal Saline (0.9% NaCl) |
|---|---|---|---|
| Preservative | 0.9% benzyl alcohol | None | None (unless bacteriostatic saline) |
| Multi-use? | Yes — up to 28 days after first puncture | Single use only | Single use only (unless bacteriostatic) |
| Peptide compatibility | Compatible with virtually all peptides | Compatible but no protection | Some peptides may precipitate in saline |
| Use within | 28 days (refrigerated) | 24 hours | 24 hours |
| Best for | All peptide reconstitution (standard choice) | Single-use applications only | Specific protocols requiring isotonic solution |
The bottom line: BAC water is the default choice for peptide reconstitution in research settings. Sterile water is acceptable for single-use applications but offers no protection for multi-use vials. Normal saline is rarely needed unless a specific protocol requires it, and it can cause precipitation with some peptides.
How to Use Bacteriostatic Water for Peptide Reconstitution
Basic Protocol
- Allow the peptide vial to reach room temperature (15-20 minutes from freezer)
- Wipe both the BAC water vial and peptide vial stoppers with alcohol swabs
- Draw the calculated volume of BAC water into a sterile syringe
- Inject BAC water slowly down the inside wall of the peptide vial — never directly onto the powder
- Gently swirl until dissolved — never shake
- Refrigerate immediately after reconstitution
For a detailed step-by-step guide with reconstitution volume tables, see our Complete Reconstitution Guide.
Need help calculating exact volumes? Use our free Peptide Reconstitution Calculator to instantly determine concentration and dose volume for any peptide.
Storage and Handling
Before opening: Store BAC water at room temperature (15-30°C). It does not require refrigeration before first use. Keep in original packaging, protected from light.
After first puncture: BAC water can be used for up to 28 days after the first needle puncture, provided the rubber stopper is wiped with alcohol before each use and the vial is stored in a clean environment. After 28 days, discard any remaining volume.
Reconstituted peptides: Once BAC water is mixed with a peptide, store the reconstituted solution at 2-8°C (refrigerator) and use within 28 days. See our Peptide Storage Guide for complete storage protocols.
Quality Matters: Hospira BAC Water
Not all BAC water is created equal. PSPeptides carries Hospira (Pfizer) bacteriostatic water — pharmaceutical-grade, USP-certified, and manufactured under the same quality standards as products used in clinical settings. Hospira BAC water is the industry standard for peptide reconstitution because of its consistent quality, sterility assurance, and reliable 0.9% benzyl alcohol concentration.
Avoid purchasing BAC water from unverified sources. Off-brand BAC water may have inconsistent preservative concentrations, questionable sterility, or contaminants that could degrade your peptides or introduce variables into your research.
Reconstitution Quick Reference
| PSPeptides Product | Recommended BAC Water | Concentration |
|---|---|---|
| Retatrutide 5mg | 2.5mL | 2mg/mL |
| GHK-Cu 50mg | 2.0mL | 25mg/mL |
| GLOW 70mg | 3.5mL | 20mg/mL |
| KLOW 80mg | 4.0mL | 20mg/mL |
Buy Hospira Bacteriostatic Water — $19.99 → | Buy Laboratory Syringes →
Frequently Asked Questions
Can I use tap water or distilled water to reconstitute peptides?
No. Tap water contains minerals, chlorine, and microorganisms that will contaminate and degrade the peptide. Distilled water lacks sterility assurance. Only use bacteriostatic water or sterile water for injection (USP-grade) for peptide reconstitution.
How long does reconstituted peptide last in BAC water?
Approximately 28 days when stored at 2-8°C (refrigerated). The benzyl alcohol preservative maintains antimicrobial protection for this period. After 28 days, bacterial growth may compromise the solution even with the preservative present.
Does BAC water need to be refrigerated?
Before opening: no, room temperature storage is fine. After first puncture: still acceptable at room temperature, but refrigeration extends the usable life. Reconstituted peptides (BAC water + peptide) should always be refrigerated at 2-8°C.
How much BAC water do I need?
One 10mL vial of BAC water is typically sufficient to reconstitute 2-4 peptide vials, depending on the reconstitution volume used. For most researchers, purchasing one BAC water vial per 2-3 peptide vials is appropriate.
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