Bacteriostatic water vs sterile water comes down to one ingredient: a preservative. Both start as sterile water, but bacteriostatic water contains benzyl alcohol, which slows bacterial growth after the vial has been opened. That single difference affects how long a vial can be used and which laboratory methods it suits.
What is bacteriostatic water?
Bacteriostatic water is sterile water with 0.9% (9 mg/ml) benzyl alcohol added. “Bacteriostatic” means it slows the growth of bacteria but does not necessarily kill them. It is not a sterilising agent, so good aseptic technique still matters. Chemical data for the preservative is available from PubChem.
What is sterile water?
Sterile water has been treated to remove living organisms and has no preservative added. Once a container has been opened, there is nothing to slow contamination, so it is typically treated as single-use and any remainder is discarded.
Bacteriostatic water vs sterile water at a glance
| Feature | Bacteriostatic water | Sterile water |
|---|---|---|
| Preservative | 0.9% benzyl alcohol | None |
| Typical use pattern | Multi-use vial | Single use |
| After first puncture | Commonly up to 28 days, check the label | Discard remainder |
| Main limitation | Preservative may affect some methods | Contamination risk once opened |
How to choose for laboratory work
Choose bacteriostatic water when you need to withdraw from one vial several times and your method tolerates benzyl alcohol. Choose sterile water when any additive could interfere with your results, or when you will use the full volume at once. Benzyl alcohol can affect some sensitive materials and cell-based work, so check your method or protocol first. If you are unsure, run a small compatibility test before committing valuable material.
How should you handle a multi-use vial?
- Label the vial with the date of first puncture.
- Disinfect the stopper before each withdrawal.
- Use a new sterile needle or tip each time.
- Store it as the label directs and discard it after the in-use period.
- Discard it straight away if the liquid looks cloudy or contains particles.
Frequently asked questions
Can bacteriostatic water be used forever once opened?
No. The preservative slows bacterial growth but does not last indefinitely. Follow the in-use period on the label, which is commonly up to 28 days after first puncture.
Is bacteriostatic water the same as distilled water?
No. Distilled water has been purified by distillation but is not necessarily sterile, and it contains no preservative.
We sell bacteriostatic water in 3ml and 10ml vials for laboratory use only. They are not for human or veterinary use. See all our laboratory supplies.
