What is Bacteriostatic Water? (Peptide Glossary)

Bacteriostatic water (often called BAC water) is sterile water for injection with 0.9% benzyl alcohol added. The benzyl alcohol is the key ingredient: it inhibits bacterial growth inside the vial, which is essential because research protocols typically involve drawing from the same vial multiple times over days or weeks. Each needle puncture is a contamination opportunity, and the preservative is the defense.

The alternative, sterile water for injection, contains no preservative. It is appropriate only for single-use reconstitution - once opened, any remaining solution should be discarded. Using plain sterile water for a multi-use vial invites bacterial contamination that can degrade the peptide and compromise research results.

A small number of peptides have compatibility concerns with benzyl alcohol and are better reconstituted with 0.6% acetic acid solution - check the compound's research literature or the supplier's guidance. BAC water itself is inexpensive and widely sold by peptide suppliers; it is also one of the simplest products for a vendor to quality-control, so a supplier whose BAC water arrives cloudy or unsealed is telling you something about their standards.