Bacteriostatic water is a sterile, nonpyrogenic preparation of water for injection containing 0.9% (9 mg/mL) benzyl alcohol as a bacteriostatic preservative. It is widely used in research and clinical laboratory settings as a diluent for the reconstitution of lyophilized peptides, proteins, and other research compounds that require a sterile aqueous vehicle.

The inclusion of benzyl alcohol as a preservative inhibits microbial growth, allowing reconstituted solutions to be stored and used over multiple doses for up to 28 days when refrigerated at 2-8°C. This distinguishes bacteriostatic water from sterile water for injection, which contains no preservative and must be used as a single-dose preparation.

Supplied as a sterile solution in sealed vials. Intended for use as a research diluent only.