Bacteriostatic Water for Peptides
What it is, why it matters, and where to get it.
What Is Bacteriostatic Water?
Bacteriostatic water (BAC water) is sterile water for injection containing 0.9% benzyl alcohol as a preservative. The benzyl alcohol inhibits bacterial growth, making the vial safe for multiple draws over time when handled under proper sterile conditions.
It is the standard diluent used in the research community for reconstituting lyophilized peptides including BPC-157, TB-500, retatrutide, semaglutide, and others.
Why Not Regular Sterile Water?
Plain sterile water for injection contains no preservative. Once the rubber stopper is punctured, repeated needle entries introduce contamination risk with no preservative to inhibit bacterial growth. For single-draw use only.
Bacteriostatic water's 0.9% benzyl alcohol preservative allows multi-dose use when proper sterile technique is followed. For any research protocol requiring multiple draws from a reconstituted vial, bacteriostatic water is the appropriate choice.
Bacteriostatic Water vs. Sterile Water
Both are USP-grade sterile water for injection, but bacteriostatic water contains 0.9% benzyl alcohol as a preservative. That preservative is what allows a reconstituted vial to be drawn from multiple times over the following weeks without bacterial growth turning it into a contamination risk.
Shelf life is the practical difference. Plain sterile water for injection is single-draw only — discard the vial after one use once the stopper is punctured. Bacteriostatic water, once opened and refrigerated with sterile technique, is typically considered good for up to 28 days per the USP monograph. For any peptide protocol that dispenses more than one dose from a reconstituted vial, bacteriostatic water is the appropriate diluent.
Bacteriostatic Water by Compound
BAC water is the same diluent across compounds, but a few practical notes are worth flagging. See the peptide dosage chart for typical vial size and BAC water volume per compound.
| Compound | Handling Note |
|---|---|
| GHK-Cu | Reconstituted solution takes on a normal blue tint from the copper complex — expected, not contamination. Larger vials (typically 50 mg) usually pair with 5 mL of BAC water. |
| Retatrutide | Higher-milligram vials (typically 10 mg) with weekly doses in the multi-mg range make precise BAC water volume important — small mL differences shift the per-dose draw meaningfully. |
| Tirzepatide | Same class of higher-strength vial. Weekly dosing means the vial sits reconstituted for several draws, so multi-dose bacteriostatic water is essential. |
| BPC-157 | Dosed in micrograms rather than milligrams. Reconstitution volume determines the mcg/mL concentration and the syringe unit reading — a small BAC water change is a large per-dose change. |
| PT-141 | Often reconstituted with a smaller BAC water volume (around 1 mL for a 10 mg vial) to keep the as-needed draw small. Precise measurement matters. |
| Ipamorelin / CJC-1295 | Multiple daily draws from the same reconstituted vial — bacteriostatic water (not sterile) is required for this dosing pattern. |
What to Look For
- 0.9% benzyl alcohol concentration — verify on the label
- USP grade — pharmaceutical standard
- 30 mL multi-dose vial — sufficient for most research protocols
- Third-party tested supplier — COA available
Sourcing
Recommended Source
PSPeptides carries USP-grade bacteriostatic water, third-party tested. Ships domestically. Use code BANANAS10 for 10% off.
Get BAC Water →Affiliate link — The Protocol Kit earns a commission at no extra cost to you.
Frequently Asked Questions
Once you have your BAC water, use the free calculator to determine exactly how much to add to your vial.
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