Comparison

Bacteriostatic water vs sterile water

The most consequential decision in reconstitution, and the one most often made without thinking. The difference is a preservative, and it determines how many times a vial can be entered.

What is the difference between bacteriostatic and sterile water?

Bacteriostatic water is the default and should be the assumed choice unless there is a specific reason against it. The benzyl alcohol suppresses microbial growth, which is what allows one vial to be drawn from repeatedly over weeks. Sterile water is correct only when that preservative would interfere, and using it for a multi-entry vial turns the solution into a growth medium.

Side by side

Property	Bacteriostatic Water	Sterile Water
Preservative	0.9 percent benzyl alcohol	None
Repeat entry	Suitable for repeated withdrawal	Single use only
Usable window once opened	Weeks, refrigerated	Use immediately, discard the remainder
Typical format	30 ml multi-dose vial	10 ml single-use ampoules
When it is wrong	Where benzyl alcohol interferes with the compound or the assay	Where a vial must be entered more than once
Default choice	Yes, for most reconstitution	Only when the preservative is a problem
Price	$16.00 · 30 ml	$16.00 · 10 ml x 10

Both compounds

Bacteriostatic Water

30 ml

Sterile water with 0.9 percent benzyl alcohol, 30 ml vial.

Storage: Ambient

Sterile Water

10 ml x 10

Preservative-free sterile water, 10 ml ampoules, 10 per pack.

Storage: Ambient

Questions

Can sterile water be used to reconstitute a peptide?

Yes, but it carries no preservative, so the vial must be used immediately and the remainder discarded. For anything entered more than once, bacteriostatic water is the correct choice.

What does benzyl alcohol actually do?

It is a bacteriostatic preservative: it suppresses microbial growth rather than killing what is already present. That is what makes repeated entry into one vial acceptable over a period of weeks.

Does bacteriostatic water affect the peptide?

For most compounds, no. For a minority it can interfere with the compound or with a downstream assay, and in those cases preservative-free sterile water is used instead and handled as single use.

Other comparisons

All products listed are sold strictly for in-vitro laboratory research and analytical use. They are not drugs, foods, cosmetics or medical devices, and are not intended to diagnose, treat, cure or prevent any disease.