When reconstituting peptides, the choice of solvent is as important as the peptide itself. The two most common options are Bacteriostatic Water and Sterile Water. While they look identical, their safety profiles for research are vastly different. Refer to the peptide reconstitution guide for procedure details.
Bacteriostatic Water ("Bac Water")
Composition: Sterile Water + 0.9% Benzyl Alcohol
The 0.9% benzyl alcohol acts as a preservative. It creates an environment where bacteria cannot reproduce (hence "bacteriostatic"—stopping bacteria).
- Shelf Life: Once opened/punctured, a vial of Bac Water (or a peptide mixed with it) remains safe to use for approximately 28 days.
- Use Case: Mandatory for any multi-dose vial. If you plan to use the peptide more than once, you must use Bac Water.
Sterile Water for Injection (SWFI)
Composition: 100% Sterile Water (No additives)
This water is sterilized during manufacturing but contains no preservatives to keep it that way once the seal is broken.
- Shelf Life: Once punctured, it is theoretically susceptible to bacterial growth immediately. Clinical guidelines often say to discard within 4 hours.
- Use Case: Only for single-use vials where the entire content is administered immediately and the vial is discarded.
Why Benzyl Alcohol Matters
Every time you insert a needle into a vial, you introduce a tiny risk of contamination from the air or the needle surface. In sterile water, a single bacterium can multiply into millions within days. In bacteriostatic water, the alcohol prevents this growth, keeping your research subject safe for the duration of the protocol. Correct storage is also key—see peptide storage guidelines.
Math doesn't change regardless of water type: learn how to calculate peptide concentration or use the ultimate reconstitution calculator. And always ensure you are reading an insulin syringe correctly.