The Short Answer
For multi-day or multi-dose research applications, use bacteriostatic water. For single-use protocols completed within 24 hours of reconstitution, either works. The decision comes down to whether the experimental endpoint can tolerate trace benzyl alcohol.
What’s In Each
Bacteriostatic water is sterile water containing 0.9% benzyl alcohol as a preservative. The benzyl alcohol inhibits microbial growth, allowing the solution to remain usable across multiple needle insertions over 14–28 days at refrigerated temperatures. Sterile water contains nothing but water — no preservatives, no additives, no buffering agents.
Why Benzyl Alcohol Works
Benzyl alcohol disrupts microbial cell membranes at the 0.9% concentration. It is not a strong antimicrobial like an antibiotic, but it is sufficient to prevent bacterial proliferation in a sealed multi-dose vial under refrigerated conditions. The preservative remains effective for the full labeled storage period.
When to Avoid Benzyl Alcohol
Some research endpoints are sensitive to benzyl alcohol or related solvents. If your assay involves cellular models susceptible to membrane disruption, or if the research protocol explicitly requires preservative-free conditions, use sterile water. The trade-off is single-use only — once the sterile water vial is pierced, the reconstituted peptide must be used within 24 hours.
Storage After Reconstitution
Bacteriostatic-reconstituted peptide: 14–28 days at +2 to +8 °C. Sterile-water-reconstituted peptide: 24 hours maximum at +2 to +8 °C. For longer storage of sterile-water solutions, aliquot immediately and freeze at -20 °C. See our full storage protocol for temperature ranges across compound types.
Concentration Math
Once you’ve chosen your water type and reconstitution volume, see our guide on calculating reconstitution concentrations — covers mg/mL math, IU conversion for insulin syringes, and blend-vial calculations.
VialPepLab Starter Kit
Our Research Starter Kit includes 30 mL of bacteriostatic water alongside sterile syringes and alcohol swabs — the standard supplies for laboratory reconstitution work. Available in the main catalog. Sterile water is available separately on request — contact us for availability.
Full reconstitution walkthrough: Storage & Reconstitution page.