Quick answer
Bacteriostatic water is sterile water with 0.9% benzyl alcohol added, which stops bacteria multiplying in the bottle once it has been opened. That is why a bac water vial is good for about 28 days after the first puncture while a sterile water vial is single-use. If you will draw from the mixed vial more than once, you want bacteriostatic water. Neither is saline, and neither is tap or bottled water.
Side by side
Rows that differ are highlighted. Values come from the product records for the two products named in the header.
Bacteriostatic water Bac Water (Bacteriostatic Water), 30 mL |
Sterile water Sterile Water for Injection |
|
|---|---|---|
| LiquidBacteriostatic water has a preservative and keeps 28 days once opened. Sterile water and saline have none and are single-use. Glossary | Bacteriostatic water | Sterile water |
| Preservative0.9% benzyl alcohol stops bacteria multiplying in an opened bottle. It is what makes a multi-dose bottle possible. Glossary | Yes | No |
| Volume | 30 mL | 10 mL |
| Single-use | No | Yes |
| Once openedHow long the bottle is considered good after the first needle goes through the stopper. | 28 days | 0 days |
| PriceRough position within its category, not a live price: budget is the cheapest sensible option, premium costs more for a reason the page explains. | Budget | Budget |
| TravelWhether it is practical to fly with: carry-on means it goes through security without fuss. | Carry-on friendly | Carry-on friendly |
| SterileIndividually sealed and sterile until opened. Anything that touches the inside of a vial or your skin should be. | Yes | Yes |
| PackHow many you get. Check this against the photo; Amazon listings often show ten and ship one. | 1 | 1 |
| Reusable | No | No |
Which should you choose?
- Pick bacteriostatic water for anything you will draw from over days or weeks. This is the everyday choice.
- Pick sterile water only for a vial you will use all at once, or where the product's own instructions say benzyl alcohol is not wanted.
- Neither is for nasal sprays; that is what sterile saline is for.
The products
Open in the comparison tool Find the right mixing water
Related guides
- Bac water vs. sterile water (and which to buy)
- How long does bac water last once opened?
- Cloudy vials and reconstitution mistakes: what went wrong, and what can be saved
Common questions
Can I use sterile water instead of bacteriostatic water?
For a single use, yes. For a vial you keep, no: nothing stops bacteria growing in it.
How long does bacteriostatic water last once opened?
About 28 days; write the date on the vial.
Is saline the same as sterile water?
No. Saline is 0.9% salt in water, used for nasal preparations; sterile water has nothing in it.
Reviewed 2026-09-03. Equipment comparison only; nothing here is advice about what to inject or how much. Affiliate links open your own country's Amazon store; your price is the same.