What is bacteriostatic water?

Bacteriostatic water is sterile water with a small amount of a preservative, most commonly benzyl alcohol, added at a low concentration. On its own, sterile water contains no bacteria at the moment it is sealed, but it also contains nothing to stop bacteria from growing once the seal is broken. Bacteriostatic water is built for exactly that moment: the point where a sealed vial gets opened, accessed, and set aside for later use.

The word "bacteriostatic" describes what the preservative does. It does not kill bacteria outright the way a disinfectant might. Instead, it inhibits bacterial growth and reproduction, holding a population in check rather than eliminating it. That distinction matters in a laboratory setting where a vial may be accessed more than once: a bacteriostatic diluent is formulated to resist contamination across repeated draws, not just at the moment of first use.

Plain sterile water, by contrast, is typically intended for a single use once opened. Without a preservative, there is nothing to slow microbial growth after the seal is broken, so it is generally treated as compromised once air, a needle, or any outside surface has touched the contents.

Where it is used as a diluent

In laboratory workflows, bacteriostatic water is commonly used as a diluent, meaning it is added to another substance to dissolve or dilute it to a working concentration, rather than being the material of interest itself. A sealed vial of diluent sitting on a bench for the length of a research project depends on that bacteriostatic property to remain usable throughout.

Reconstitution Solution is prepared this way: sterile filtered water with benzyl alcohol added as the preservative, sealed in glass. See our product page for the specific preparation and available sizes, or read about what benzyl alcohol does in more detail.