Bacteriostatic Water vs Sterile Water: What's the Difference?
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- Bacteriostatic water contains 0.9% benzyl alcohol; sterile water has no preservative.
- Bacteriostatic presentations are labelled multi-dose; preservative-free sterile water presentations are labelled single-dose.
- Both supplied presentations are labelled sterile.
- A qualified healthcare professional must select the compatible diluent using the relevant product information.
No — bacteriostatic water and sterile water are not the same. Both are sterile, but bacteriostatic water (often written BAC water) contains 0.9% benzyl alcohol as a preservative and is labelled multi-dose, while sterile water contains no preservative and is labelled single-dose. That one difference is the whole answer; everything below explains it.
This comparison is general information. A qualified healthcare professional must select the appropriate diluent for clinical use.
The short answer
Both start as sterile, purified water filtered to remove microorganisms. The difference is the preservative: bacteriostatic water contains 0.9% benzyl alcohol; sterile water contains nothing but water. That single addition changes how the vial is used — repeated access versus one withdrawal and discard.
Side-by-side comparison
| Bacteriostatic Water (BAC Water) | Sterile Water | Bacteriostatic Saline | |
|---|---|---|---|
| Composition | Water + 0.9% benzyl alcohol | Purified water only | 0.9% NaCl + benzyl alcohol |
| Preservative | 0.9% benzyl alcohol | None | 0.9% benzyl alcohol |
| Vial use | Multi-dose — repeated access | Single withdrawal, then discard | Multi-dose — repeated access |
| Use after opening | Repeated access from the sealed vial | Use promptly, do not re-enter | Repeated access from the sealed vial |
| Isotonic | No | No | Yes (0.9%) |
| Manufacturer-labelled as sterile | Yes | Yes | Yes |
| Selection | Use only where the medicine information and a qualified healthcare professional specify the presentation | ||
| Vial | Buy BAC water 30 mL | Sterile water | Bacteriostatic sodium chloride |
The same products, different names
Much of the confusion here is vocabulary rather than chemistry. These all refer to the same two products:
- Bacteriostatic water = BAC water = bac water = bacteriostatic water for injection = BWFI.
- Bacteriostatic sodium chloride = BAC sodium chloride = BAC saline = bacteriostatic saline.
- Sterile water is not the same as distilled water. Distilled water describes a purification method; sterile water describes a manufactured, filled and sealed sterile presentation. That distinction has its own guide: sterile water vs distilled water.
Bacteriostatic water, explained
Bacteriostatic water is sterile water with 0.9% (9 mg/mL) benzyl alcohol added. The manufacturer describes benzyl alcohol as a bacteriostatic preservative that inhibits the growth of most potentially contaminating microorganisms. The presentation is labelled multi-dose, but the preservative does not replace labelled handling requirements or aseptic technique by a qualified professional.
Sterile water, explained
Sterile water is preservative-free and is supplied in single-dose presentations. Follow the exact vial label and product information; do not treat a single-dose presentation as multi-dose.
Where saline fits in
There is a third option worth knowing: bacteriostatic sodium chloride 0.9%. It is isotonic saline with a bacteriostatic preservative. Its clinical application depends on the specific manufacturer-labelled presentation and the direction of a qualified healthcare professional.
How is the presentation selected?
- Bacteriostatic water: water with 0.9% benzyl alcohol in a labelled multi-dose presentation.
- Sterile water: preservative-free water in a labelled single-dose presentation.
- Bacteriostatic sodium chloride 0.9%: isotonic saline with a bacteriostatic preservative.
Only the relevant medicine information and a qualified healthcare professional can determine which presentation is compatible for a clinical application. These are diluents, not ready-to-administer medicines; never inject them by themselves or self-administer.
Buying either presentation in Australia
Availability is the practical difference most buyers hit first. Preservative-free sterile water ampoules are a common pharmacy line; the bacteriostatic presentations rarely are, so they are usually bought online. We stock both preserved lines in original factory-sealed manufacturer vials — bacteriostatic water (BAC water) and bacteriostatic sodium chloride 0.9% (BAC saline) — dispatched from Melbourne with tracked Australia-wide delivery. What to check before buying from anyone, including us, is covered in where to buy bacteriostatic water in Australia.
Not sure which vial you need?
Browse original, factory-sealed bacteriostatic water, sterile water and saline presentations.
Shop BAC water and diluents →Frequently asked questions
Is bacteriostatic water the same as sterile water?
No. Both are sterile, but bacteriostatic water contains 0.9% benzyl alcohol while sterile water has no preservative. The preservative is what allows a bacteriostatic vial to be entered repeatedly.
Is BAC water the same as sterile water?
No. BAC water is simply the abbreviation for bacteriostatic water, which contains 0.9% benzyl alcohol and is labelled multi-dose. Sterile water is preservative-free and labelled single-dose.
Is bacteriostatic water the same as saline?
No. Bacteriostatic water is preserved water with no salt content. Bacteriostatic sodium chloride — also called BAC saline — is isotonic 0.9% salt solution with the same preservative.
Is sterile water the same as distilled water?
No. Distilled water describes a purification method and is not supplied as a sterile medical presentation. Sterile water for injection is manufactured, filled and sealed as a sterile product under its own labelling.
Can bacteriostatic water and sterile water be used interchangeably?
No — do not assume they are interchangeable. They differ in preservative content and in labelled vial use (multi-dose versus single-dose), and the compatible diluent for any preparation is stated in that medicine's own product information, confirmed by a qualified healthcare professional.
Is bacteriostatic sodium chloride the same as bacteriostatic water?
No. Both carry the same 0.9% benzyl alcohol preservative, but bacteriostatic sodium chloride is isotonic 0.9% saline while bacteriostatic water contains no solute at all.
Which vial should I choose?
Use only the presentation specified in the relevant medicine information by a qualified healthcare professional. This comparison is general product information, not a selection instruction.
Aus BAC Supply is an independent retailer of unopened manufacturer presentations. These products are diluents or solvents, not ready-to-administer medicines. Never inject a diluent by itself or self-administer. Compatibility, preparation and use must follow the supplied manufacturer information under qualified healthcare-professional direction. This article is general information, not medical advice. Aus BAC Supply is an independent retailer and is not affiliated with, endorsed by or an authorised distributor of the manufacturer; the name identifies the genuine factory-sealed product supplied.