Bacteriostatic water: how much to use
Reviewed by the Rite Aid Health Team · Last updated July 2, 2026
Bacteriostatic water is the liquid used to reconstitute most peptides. Here is what it is, how much to use, and why the amount changes your dose.
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What it is
Bacteriostatic water is sterile water with about 0.9% benzyl alcohol added as a preservative. The benzyl alcohol stops bacteria growing, which is what lets a mixed vial be used across several weeks in the fridge.
How much to add
- There is no single correct amount — 1 to 3 mL is typical.
- More water = more units per dose, which makes small doses easier to measure.
- Less water = fewer, more concentrated units.
- The amount does not change how much peptide is in the vial, only how you measure each dose.
Bacteriostatic vs sterile vs saline
Sterile water and saline have no preservative, so a vial mixed with them is meant for a single use. Bacteriostatic water is preferred for multi-dose vials. Follow whatever your prescriber or the product labelling specifies.
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For general education only — not medical advice or a treatment recommendation. Peptides are not a substitute for care from a licensed provider. Talk to a qualified healthcare professional before you start, stop, or change any peptide, medication, or supplement.
FAQ
A common choice is 2 mL, which makes 2.5 mg/mL — a 250 mcg dose then comes out to 10 units on a U-100 syringe. Use the calculator to try other volumes.
Yes, that is what the preservative is for — as long as you clean the stopper each time and store it as directed.
No. The total peptide is unchanged; more water just spreads it across more volume, so each dose is a larger number of units.