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Bacteriostatic Water vs Sterile Water: Which to Use for Reconstitution

Both dissolve a lyophilised peptide — but they're not interchangeable. The difference comes down to one additive and how long the solution needs to last.

The quick answer

• Bacteriostatic water contains 0.9% benzyl alcohol, which inhibits bacterial growth — so a reconstituted solution stays usable in the fridge for longer (commonly ~4 weeks).
• Sterile / distilled water has no additives — fine for a single-session use where the solution won't be stored (commonly within ~24–48 hours).
• Rule of thumb: multi-use over days/weeks → bacteriostatic; one-and-done → sterile.

What each one actually is

Bacteriostatic water

Water containing a small amount (0.9%) of benzyl alcohol as a bacteriostatic agent. The alcohol suppresses microbial growth, which is why a vial reconstituted with it can be drawn from repeatedly over several weeks when refrigerated.

Sterile / distilled water

Purified water with no preservatives. It's sterile at the point of use but offers no ongoing protection against contamination once the vial is opened, so any solution made with it should be used quickly.

Side by side

How to reconstitute cleanly (either solvent)

1. Sanitise both vial stoppers with an alcohol swab and let them dry.
2. Draw the volume of solvent you've calculated for your target concentration.
3. Add it slowly — let the solvent run down the inside wall of the vial, never directly onto the powder.
4. Dissolve gently — swirl or leave to stand; do not shake.
5. Label & refrigerate — mark compound, concentration and date, then store at 2–8 °C.

A note on solubility

A few compounds don't dissolve readily in water and need a specific solvent (for example a mild acetic-acid solution). Always check the individual compound's profile before reconstituting.