Bacteriostatic water (BAC water)

Bacteriostatic water - often shortened to „bac water" - is sterile water with 0.9% benzyl alcohol. „Bacteriostatic" means the alcohol inhibits microbial growth: it slows the multiplication of germs rather than necessarily killing them. This way, a mixed solution (the prepared liquid after adding the powder) typically stays usable for up to about 28 days when refrigerated.

Why it is the standard mixing liquid

The reason is practical: peptide vials (small glass vials containing short protein-based active ingredients, used in research and in some therapies) are pierced repeatedly over days to weeks. That requires a preservative, and that is exactly what the benzyl alcohol provides.

Common mistakes & limits

• Confusing it with sterile water - which has no preservative and is meant for immediate single use.
• Benzyl alcohol is problematic for newborns and some people are sensitive to it.

Wording mix-ups

Short „bac water"; not the same as „water for injection", which is sterile water without any additive.