BAC water for peptides
The essentials
- BAC water is sterile water plus 0.9% benzyl alcohol, a preservative.
- The preservative is why a mixed vial lasts weeks of repeated draws, not one use.
- Sterile water and saline work but are single-use; never use tap or bottled water.
- How much to add depends on your vial strength and the amount you measure.
Why bacteriostatic water is used for peptides
Peptides arrive as a dried, lyophilized powder. Before you can measure any amount, the powder has to be dissolved in a liquid, a step called reconstitution. The liquid you add is the diluent, and for peptides that diluent is almost always bacteriostatic water.
What sets it apart is the benzyl alcohol. It slows bacterial growth, so a mixed vial can be entered again and again over several weeks instead of being thrown out after one use. Because peptide amounts are typically measured out over many draws, that multi-dose practicality is exactly what you want.
What not to use
Plain sterile water for injection and saline can dissolve a peptide, but neither contains a preservative, so the vial is single-use and should not be stored and re-entered. Bacteriostatic water is preferred precisely because it can be. Tap water and bottled water are never appropriate, they are not sterile.
How much bacteriostatic water to add
There is no single right amount. The water sets the concentration: more water makes a weaker solution you measure more of, less water makes a stronger one you measure less of. The goal is an amount that lands your measurement on a clean, readable mark on the syringe. A common starting point is 2 mL for a 5 mg vial, which makes 2.5 mg/mL.
Storing the mixed vial
Once mixed, most peptides are kept refrigerated and out of light, and an opened multi-dose vial is commonly dated and discarded within a few weeks. How long a specific peptide lasts depends on the compound, so follow the instructions that came with your product rather than a general figure.
BAC water for peptides FAQ
Is bacteriostatic water good for peptides?
Yes. Bacteriostatic water is the standard reconstitution solution for peptides. Its benzyl alcohol preservative holds bacteria back, so a reconstituted vial stays usable for weeks of repeated draws rather than a single use, which suits how peptides are measured out over time.
Can you use sterile water or saline instead of bacteriostatic water for peptides?
You can dissolve a peptide in sterile water or saline, but neither has a preservative, so the mixed vial is single-use and should not be stored and re-entered. Bacteriostatic water is preferred for multi-dose vials because the preservative lets you draw from it repeatedly. Never use tap or bottled water.
How much bacteriostatic water do you use for a peptide?
Enough that your measurement lands on a clean mark on the syringe. There is no fixed amount, it depends on the vial strength and how much you want to measure. A common starting point is 2 mL for a 5 mg vial, which makes 2.5 mg/mL. Use a calculator to get the exact amount for your vial.
What is a reconstitution solution?
A reconstitution solution is the sterile liquid you add to a dried (lyophilized) powder to dissolve it into a measurable form. For peptides, that solution is almost always bacteriostatic water; the preservative is what makes a multi-dose vial practical.
Is bacteriostatic water the same as water for injection?
No. Sterile water for injection has no preservative and is intended for single use. Bacteriostatic water is the same sterile water with 0.9% benzyl alcohol added, which lets a vial be entered more than once. It is not safe for newborns.
Ready to mix?
The peptide calculator turns your vial amount and the amount you want to measure into the exact bac water to add, the concentration, and your syringe units, with every step shown.