What bacteriostatic water is
Bacteriostatic water is United States Pharmacopeia (USP) sterile water with one addition: 0.9% benzyl alcohol, an antimicrobial preservative. The benzyl alcohol does not kill organisms outright — it holds bacterial growth in check (hence bacterio-static), which is exactly what you want in a vial you will sample from more than once. That property is the entire reason it is the default solvent for reconstituting lyophilized research peptides rather than plain sterile water, which has no preservative and should be discarded immediately after a single use.
For research peptides specifically, the workflow is always the same: the compound is shipped as a freeze-dried (lyophilized) powder for stability, then dissolved in bacteriostatic water immediately before in-vitro work. The peptide does not change; you are simply rehydrating it into a measurable liquid stock.
The peptide reconstitution calculator, in one equation
Despite the name, a peptide reconstitution calculator is not a black box. It runs one relationship in three directions. Get this and you never need the tool:
- Concentration (mg/mL) = peptide mass (mg) ÷ water volume (mL)
- Draw volume (mL) = target amount ÷ concentration
- Doses per vial = total peptide mass ÷ target amount
Worked example. You reconstitute a 10 mg vial in 2 mL of bacteriostatic water: concentration = 10 ÷ 2 = 5 mg/mL (5,000 µg/mL). To withdraw a 250 µg research aliquot: 250 ÷ 5,000 = 0.05 mL, i.e. 5 units on a U-100 insulin syringe. The vial holds 10,000 µg ÷ 250 µg = 40 aliquots. Every reconstitution problem collapses to those three lines.
Volume reference table
The table below shows the final concentration for common vial sizes and water volumes. Pick the row that makes your target amount easy to measure on a syringe.
| Vial mass | Bacteriostatic water | Concentration | 1 unit (0.01 mL) = |
|---|---|---|---|
| 5 mg | 2 mL | 2.5 mg/mL | 25 µg |
| 10 mg | 1 mL | 10 mg/mL | 100 µg |
| 10 mg | 2 mL | 5 mg/mL | 50 µg |
| 10 mg | 3 mL | 3.33 mg/mL | 33 µg |
| 15 mg | 3 mL | 5 mg/mL | 50 µg |
| 30 mg | 3 mL | 10 mg/mL | 100 µg |
How to reconstitute, step by step
- Let the peptide vial and the bacteriostatic water reach room temperature (15–20 minutes).
- Wipe the rubber stopper of both the peptide vial and the water vial with a fresh alcohol swab.
- Decide your target concentration, then use concentration = mass ÷ volume to find how much water to add.
- Draw that volume of bacteriostatic water into a sterile insulin syringe.
- Rest the needle on the inner glass wall and let the water run down slowly — never spray it onto the powder.
- Roll or swirl the vial gently between your palms until fully dissolved. Do not shake.
- Inspect for a clear (or, for GHK-Cu, blue) particulate-free solution before any withdrawal.
- Label the vial with the concentration and date, store at 2–8 °C, and use within the compound’s stability window.
Storage and stability
Once reconstituted, store the solution at 2–8 °C and use it within the compound's stability window — commonly around 28 days, matching the benzyl-alcohol preservative window. The sealed lyophilized vial is best kept at -20 °C, where it stays stable for months. Keep both forms away from light and moisture. For compound-specific windows and the science behind freeze-drying, see the complete research peptides guide; for the copper peptide whose solution stays blue, see the GHK-Cu guide, and the BPC-157 dosage reference applies the same math to a regenerative peptide.