The 28-Day Rule for Opened Bac Water Vials
By the BacWater.fit team · Updated
Short answer. Once the stopper of a multi-dose vial has been punctured, the usual practice is to write the date on it and discard it 28 days later, unless the label states a different period (CDC). The benzyl alcohol in bac water slows the growth of bacteria between uses; it does not make an opened vial keep indefinitely.
Day one is the first puncture
The clock starts when the stopper is first pierced, not on the day you bought or received the vial. Unopened vials keep until the expiry date of their lot.
Why a preserved vial still has a limit
Each puncture can carry a few microbes into the vial. Benzyl alcohol at 0.9% holds bacterial growth back, but it is not a disinfectant for everything and its effect is not unlimited — hence a fixed discard date.
Sterile water and acetic acid water are different
Neither contains a preservative. Treat each vial as single use: puncture it, draw what you need, discard the rest.
Habits that help
- Write the date of first puncture on the vial or its kit.
- Swab the stopper with 70% isopropyl alcohol and let it dry before each puncture.
- Keep opened and unopened vials at 15–25 °C, away from light; never freeze them.
- Discard a vial that looks cloudy, discoloured or has particles — the specification is a clear, colourless solution.