BAC Water vs Sterile Water
The difference is one ingredient. Bacteriostatic water contains 0.9% benzyl alcohol, sterile water contains nothing but water, and that single addition is why one vial can be used for 28 days and the other has to be thrown away after one.
What is the actual difference between them?
| Bacteriostatic water | Sterile water | |
|---|---|---|
| Preservative | 0.9% benzyl alcohol (9 mg/mL) | None |
| Vial type | Multiple-dose | Single-dose |
| After first puncture | Usable for 28 days | Discard after use |
| Typical vial sizes | 10 mL, 30 mL | 10 mL, 20 mL and larger |
| Not for use in | Neonates | No preservative restriction |
| Best for | A vial drawn from over time | One preparation, used at once |
Why does the preservative change so much?
Every time a needle passes through a rubber stopper, it can carry organisms in with it. In preserved water those organisms are suppressed. In unpreserved water nothing stops them, which is the whole reason single-dose vials exist and why they say single-dose on the label.
When should you use sterile water instead?
When the entire vial is going into one preparation and nothing is being saved. In that situation the preservative buys you nothing, and sterile water is marginally cheaper.
For anything drawn from more than once, which covers nearly every reconstituted vial, bacteriostatic water is the one that works.
Is saline a third option?
Saline is a different thing again: water with 0.9% sodium chloride dissolved in it. It is not interchangeable with either, because it introduces salt into whatever you are dissolving.
Which should you buy?
For reconstitution, bacteriostatic water almost every time. The 30mL vial suits regular use and the 10mL suits occasional use. How much to add per vial is on bac water for peptides.
Frequently Asked Questions
- What is the difference between bacteriostatic and sterile water?
- Bacteriostatic water contains 0.9% benzyl alcohol and can be drawn from for 28 days after the first puncture. Sterile water contains no preservative and must be used immediately, then discarded.
- Can you use sterile water instead of bacteriostatic water?
- You can, but only if the whole vial is used in one sitting. Sterile water has nothing to suppress growth after a puncture, so re-entering the vial later is what it cannot support.
- Is sterile water cheaper than bacteriostatic water?
- Sterile water is usually slightly cheaper per vial because it contains no preservative. Bacteriostatic water is often better value in practice, because one vial covers many uses instead of one.
- Which lasts longer once opened?
- Bacteriostatic water lasts 28 days after the first puncture. Sterile water lasts as long as the single preparation you are making, and is discarded straight afterwards.
- Is saline the same as either of these?
- No. Saline is water with 0.9% sodium chloride dissolved in it. Neither bacteriostatic nor plain sterile water contains salt, and saline is not interchangeable with either for reconstitution.
- Which one should you buy for reconstitution?
- Buy bacteriostatic water if the vial will be used across more than one occasion, which covers almost every reconstituted vial. Sterile water only makes sense when the entire contents are used at once.
Important notices
Bacteriostatic water for injection, USP is a diluent used to dissolve or dilute another substance. It is not a treatment for any condition and makes no claim to be one. It contains benzyl alcohol and is not for use in neonates. Discard the vial 28 days after the first puncture.