Bacteriostatic water is sterile water for injection containing 0.9% benzyl alcohol as a preservative. The benzyl alcohol does not sterilise — it inhibits bacterial growth rather than killing existing organisms, which is what "bacteriostatic" means. That inhibition is why a reconstituted vial can be entered repeatedly over a working period instead of being discarded after one draw.
Where it fits in peptide work
It is the default solvent for multi-draw reconstitution of lyophilized research peptides. Typical laboratory practice keeps a preserved vial refrigerated and treats roughly 28 days as the conventional in-use window, mirroring the labelling convention for preserved multi-entry pharmaceutical diluents. Each entry should be through a fresh needle after wiping the stopper with an alcohol pad.
Limits worth knowing
Benzyl alcohol is not compatible with everything. It is contraindicated in neonatal preparations, it can interact with certain protein formulations by promoting aggregation, and it is generally avoided where a preservative would interfere with cell-based assays. For those situations plain sterile water or a defined buffer is the better choice.
Why it matters
Solvent choice sets how long a solution stays usable and whether repeated entry is defensible. It does not change the peptide's concentration maths.
Related terms
bacteriostatic · preservative (benzyl alcohol). Compare in bacteriostatic vs sterile water, or see Bacteriostatic Water.