Bacteriostatic water

Bacteriostatic water is sterile water for injection to which 0.9% benzyl alcohol has been added as a preservative. The alcohol does not kill bacteria outright, but it stops them multiplying, which is what allows a reconstituted vial to be punctured repeatedly over several weeks without the contents becoming contaminated. It is the diluent the research literature and the handling guides on this site assume unless a compound says otherwise.

Plain sterile water contains no preservative. It is appropriate when a vial will be used once and discarded, and it is the right choice for the small number of peptides that are unstable in the presence of benzyl alcohol, but a multi-dose vial reconstituted with it should be treated as single-use. Saline is sometimes used in clinical settings but changes the solution's ionic strength and is not the default for research handling.

Bacteriostatic water is sold in 30 mL multi-dose vials and should itself be kept clean: wipe the stopper before each draw, use a fresh needle, and discard the vial 28 days after first puncture. The reconstitution guide shows the draw and the cold-chain guide covers storage of the mixed solution.