Bacteriostatic Water: Why 0.9% Benzyl Alcohol Matters

Bacteriostatic water is sterile water with 0.9% benzyl alcohol added as a preservative. That benzyl alcohol is what lets you puncture the same vial multiple times over the course of weeks without worrying about microbial growth — and why it’s the solvent of choice for most peptide protocols.

Bacteriostatic vs. sterile water

Sterile water is a single-use reagent: once you pierce the stopper, it’s considered compromised. Bacteriostatic water is multi-dose compatible — typically 28 days after the first puncture, stored refrigerated.

How much to use

The answer is “whatever gives you convenient dose volumes.” For a 10 mg peptide vial targeting 2.5 mg per shot, 2 mL of BAC water yields 50 IU on a 1 mL insulin syringe — a comfortable draw. The calculator models this instantly.