Side-by-side comparison
Bacteriostatic Water vs Sterile Water
Bacteriostatic water vs sterile water comes down to one ingredient. Bacteriostatic water contains 0.9% benzyl alcohol and sterile water contains nothing, which allows several draws over 28 days from one vial, while sterile water is used once.
- 0.9%
- benzyl alcohol
- 3 mL
- per vial
- 28 days
- after first puncture
- 4.5–7.0
- pH range (USP)
The one difference that matters
Both start as purified, sterile water. Bacteriostatic water then receives 0.9% benzyl alcohol, and sterile water receives nothing.
Without a preservative, any bacterium that gets in when a container is opened can multiply freely. That is why sterile water is sold in single-use ampoules and the rest is thrown away after opening.
| Criterion | Bacteriostatic water | Sterile water |
|---|---|---|
| Preservative | 0.9% benzyl alcohol | None |
| Number of uses | Several draws from one vial | One, then discard |
| After opening | 28 days | Use straight away |
| Usual format | Glass vial with stopper | Glass or plastic ampoule |
| Alcohol-sensitive compounds | Not suitable | Suitable |
| Where to find it in Europe | Specialist suppliers | Pharmacies |
When bacteriostatic water makes sense
It suits work where one vial is opened several times. A reconstituted stock that will be sampled over a few weeks is the typical case.
The 28-day limit after first puncture still applies, so date the vial when you open it.
- Repeated draws from the same vial
- Compounds that tolerate benzyl alcohol
- Stocks kept in the fridge and used over several weeks
Where to buy
OXpeptides
Bac Water 3 mL
€10.90
- 3 mL glass vial, 0.9% benzyl alcohol
- Delivered in 4–6 working days, shipped from Europe
- Shipping €9.90, free on orders over €120
- 30-day returns, full refund
This water is sold and shipped by OXpeptides, from a warehouse in Europe.
When sterile water is the better pick
Choose sterile water when the compound is sensitive to benzyl alcohol, or when the whole volume is used in a single step. Some peptides and proteins lose activity or aggregate in the presence of the alcohol.
In Europe, sterile water is easy to find, since pharmacies sell it in ampoules, without preservative. Discard any leftover once the ampoule is open.
Let the reagent decide
The data sheet of the compound you are dissolving is the best guide. If it names a diluent, use that one. If it warns against preservatives, sterile water or a buffer is the safe option.
Common questions
Can I use sterile water instead of bacteriostatic water?
Yes, for most compounds. The difference is that the solution has no preservative, so plan to use it in one go or keep it short-term in the fridge according to the reagent data sheet.
Which lasts longer once opened?
Bacteriostatic water. It keeps for 28 days after the first puncture, while sterile water should be used immediately and the rest discarded.
Is sterile water easier to find in Europe?
Yes. European pharmacies routinely stock sterile water in ampoules. Bacteriostatic water is a North American format and is rarely kept in stock.
Does benzyl alcohol affect peptides?
It can. Some peptides and proteins are sensitive to it. Check the supplier data sheet and use sterile water or a buffer if it advises against preservatives.