Bacteriostatic or sterile water
Bacteriostatic water contains 0.9% benzyl alcohol, which suppresses bacterial growth and lets a reconstituted vial keep for weeks in the fridge. Sterile water has no preservative and is single-use. For anything you will draw from more than once, bacteriostatic is the one.
The difference in one line
Both are water for injection. Bacteriostatic water has a small amount of benzyl alcohol added as a preservative; sterile water has nothing added. That preservative is the whole distinction and it decides how many times you can safely put a needle through the stopper.
| Bacteriostatic | Sterile | |
|---|---|---|
| Preservative | 0.9% benzyl alcohol | None |
| Punctures | Multiple | One, then discard |
| Once opened | Weeks, refrigerated | Use immediately |
| Typical vial | 10ml or 30ml | 2ml, 5ml, 10ml |
| Best for | Anything reconstituted and used over time | Single-use preparation |
Why the preservative matters so much
Every time a needle goes through a rubber stopper it carries whatever is on the surface with it. Once is a small risk. Twenty times over a fortnight is not. Benzyl alcohol suppresses bacterial growth in between, which is what makes a multi-dose vial a sensible idea rather than a slow experiment.
This also applies to the water vial itself, not just what you mix. A 30ml bottle of bacteriostatic water lasts many mixes; a sterile ampoule is finished the moment you open it.
We do not sell bacteriostatic water. In the UK it is a prescription-only medicine, so a hardware retailer cannot supply it. Nothing on this page is a recommendation to obtain it, and where you get it is a matter for you and a pharmacist.
What not to use
- Tap water, filtered water or bottled water. Not sterile, not close.
- Boiled and cooled water. Boiling kills some organisms and leaves everything else, including whatever was in the pan.
- Saline, unless you specifically intend to and know it suits what you are mixing.
- Anything from a vial with a damaged seal or a cloudy appearance.
Questions
- How long does bacteriostatic water last once opened?
- Manufacturers typically state 28 days refrigerated after first puncture. Write the date on the vial when you open it, because you will not remember.
- Can I use sterile water instead?
- Only if you are going to use the entire reconstituted amount straight away. With no preservative, a vial you keep dipping into is a growing risk with every puncture.
- Does the benzyl alcohol affect the volume calculation?
- No. Treat 2ml of bacteriostatic water as 2ml. The preservative is a fraction of a percent and does not change the arithmetic.
3ml Glass Cartridge
One 3ml refill cartridge.