Bacteriostatic water comes up in almost every reconstitution protocol, but what actually sets it apart from plain water? In this guide we explain, research-only, what bacteriostatic water is, why it is the default choice for dissolving lyophilised peptide powder, and what to watch for when storing it.
Bacteriostatic water is water for injection with 0.9% benzyl alcohol as a preservative, which makes a vial suitable for repeated puncturing. It is the standard for reconstituting lyophilised peptide powder in the lab. For research use only, not for human or animal consumption.
What is bacteriostatic water?
Bacteriostatic water is sterile water for injection with 0.9% benzyl alcohol added. That addition inhibits bacterial growth in the vial, which sets it apart from plain water. New to peptides? First read what peptides are.
Why is it used to reconstitute peptides?
Lyophilised (freeze-dried) peptide powder needs to be dissolved before it can be used in research, and bacteriostatic water is the common choice for that. Because the preservative inhibits bacterial growth, one vial of water can be punctured for multiple reconstitutions within its shelf life — practical when a research protocol spans several sessions. The full step-by-step method is in how to reconstitute peptides.
Bacteriostatic water versus water for injection (WFI)
Water for injection (WFI) contains no preservative and is intended for single use per vial; bacteriostatic water, thanks to the benzyl alcohol, is suitable for repeated puncturing. For a single, small reconstitution, WFI is sufficient; for protocols involving multiple draws from the same vial, bacteriostatic water is the more practical and common choice in lab settings.
How do you store and use it correctly?
Bacteriostatic water should be stored refrigerated, out of light, and kept sterile, with a clean needle for each puncture of the septum. Follow the shelf life stated on the label from the moment of first use, and note the puncture date on the vial for traceability in your research log.
How much do you need?
The amount needed depends on the vial strength of the peptide and the desired concentration for your research setup. Calculate the exact ratio with the reconstitution calculator, or read the full explanation in how to reconstitute peptides. Read more about purity and batch verification in how to read a COA.
This information is general and intended solely for a research context. Peptide Lab supplies bacteriostatic water for laboratory and research purposes only. Not for human or animal consumption, not a medicine and not medical advice.
Frequently asked questions about bacteriostatic water
What exactly is bacteriostatic water?
Bacteriostatic water is water for injection with 0.9% benzyl alcohol added as a preservative. That inhibits bacterial growth, allowing a vial to be punctured multiple times within the shelf life stated on the label. For laboratory and research purposes only.
What is the difference from plain water for injection (WFI)?
Water for injection (WFI) contains no preservative and is intended for single use per vial. Bacteriostatic water contains benzyl alcohol, which allows the same vial to be punctured multiple times — practical when reconstituting several research samples from one vial of peptide powder.
How long is an opened vial of bacteriostatic water usable?
That is stated on the manufacturer's label and depends on storage conditions. General guidance is: store refrigerated, out of light, and do not use the vial beyond the stated period after the first puncture.
Is bacteriostatic water available at Peptide Lab?
Yes, as a standalone lab accessory alongside the research peptides. For laboratory and research purposes only, not for human or animal consumption.
