Bacteriostatic water vs sterile water: both are purified waters used to reconstitute lyophilised research peptides, but one contains a preservative and one does not. Here is the difference and when each is used in the laboratory.
What is bacteriostatic water?
Bacteriostatic water is sterile water that contains 0.9% benzyl alcohol as a preservative. The benzyl alcohol is bacteriostatic — it inhibits the growth of bacteria — so a single vial can be entered multiple times over a period of days to weeks without the contents spoiling. That makes it the default diluent for multi-use research reconstitution.
What is sterile water?
Sterile water (sterile water for injection, SWFI) is purified water that has been sterilised but contains no preservative. It is intended for single use: once the vial is opened there is nothing to inhibit microbial growth, so any unused portion is discarded.
Bacteriostatic water vs sterile water at a glance
| Bacteriostatic water | Sterile water | |
|---|---|---|
| Preservative | 0.9% benzyl alcohol | None |
| Vial use | Multi-use (days–weeks) | Single use |
| Best for | Repeated draws from one vial | One-time reconstitution |
| Once opened | Typically usable ~28 days, refrigerated | Discard remainder after use |
| Availability | Common research diluent | Common research diluent |
Which should you use for reconstitution?
- A vial you will draw from repeatedly → bacteriostatic water. The preservative keeps the solution stable across multiple entries.
- A single measurement, then discard → sterile water is acceptable.
- A peptide sensitive to benzyl alcohol → a minority of sequences are; check compatibility and test a small portion first.
For most research workflows bacteriostatic water is the practical choice. You can find it in our Supplies category. Once you have chosen a diluent, follow the reconstitution guide and use the reconstitution calculator to work out your concentration and syringe units.
Frequently asked questions
Is bacteriostatic water the same as sterile water?
No. Both are sterile, purified water, but bacteriostatic water also contains 0.9% benzyl alcohol as a preservative that lets a vial be used multiple times, whereas sterile water contains no preservative and is intended for single use.
Can I use sterile water instead of bacteriostatic water?
For a single reconstitution that will be used immediately, sterile water works. For a vial you will draw from repeatedly over days or weeks, bacteriostatic water is preferred because its preservative inhibits microbial growth between draws.
How long does bacteriostatic water last once opened?
A commonly cited working window is around 28 days when kept refrigerated, though you should follow the manufacturer’s stated shelf life on the specific product.
Part of our research peptides handbook.