Bacteriostatic Water for Injection, USP
BAC Water vs Sterile Water
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 the expiration date | 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. There is more on what sterile water is and where it does make sense.
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 repeatedly from the same vial. 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 good until the printed expiration date when kept refrigerated. 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 sold on this site is supplied strictly for laboratory research use only. It is not a drug, not a dietary supplement, and not intended for human or veterinary use, diagnosis, treatment, or the prevention of any condition. It may not be administered to humans or animals. By ordering you confirm you are a qualified buyer purchasing for in vitro research conducted in a controlled laboratory environment.
