The faint sweet odor is benzyl alcohol, the preservative. Bacteriostatic water is sterile WFI-grade water with 0.9% benzyl alcohol added, and benzyl alcohol is an aromatic alcohol with a characteristic mild, sweet, slightly floral or almond-like odor. At 0.9% (9 mg/mL) that odor is easy to notice when a vial is opened. It is a property of the preservative, not a sign that anything is wrong with the water.
Why plain sterile water has no odor and bacteriostatic water does
Plain sterile water contains no preservative and no dissolved organics, so it is odorless. The only ingredient that distinguishes bacteriostatic water is benzyl alcohol, so the only odor a normal vial should have is the odor of benzyl alcohol. If a vial has no detectable odor at all, that is not a defect either: odor perception varies from person to person and the smell is subtle in a small vial. Odor is not a quality-control test. The preservative content is verified by assay on the certificate of analysis (see how the preservative content is verified), and a laboratory relies on the COA and visual inspection rather than on smell.
What would not be normal
- A sharp, bitter-almond note noticeably stronger than the usual sweet odor can indicate oxidation of benzyl alcohol to benzaldehyde, which happens slowly when a vial has been open for a long time or exposed to air and light. See benzyl alcohol oxidation.
- A sour, musty or otherwise off odor, together with cloudiness, floating particles or any color, points to contamination. Such a vial is quarantined and not used. See can bacteriostatic water go bad?
- Any odor from a vial that is still sealed indicates a compromised closure, and the vial is rejected at receiving. See how to inspect a vial.
Handling note for laboratories
As with any laboratory reagent, vials are opened in a ventilated area and the safety data sheet is kept on file. See reading a safety data sheet for bacteriostatic water.
Related
Benzyl alcohol as a preservative · What is bacteriostatic water?
All BAC Water Supply products are supplied for laboratory research use only and are not for human or veterinary use.