Guide
Bacteriostatic Water vs Sterile Water
Both are sterile. Only one is made for a vial you puncture more than once.
The short answer
| Bacteriostatic water | Sterile water for injection | |
|---|---|---|
| Preservative | 0.9% benzyl alcohol | None |
| Intended use | Multiple draws from one vial | Single use, discard the rest |
| Typical label | "Multiple-dose vial" | "Single-dose" or "single-use" |
| Not for | Newborns (benzyl alcohol) | Storing and redrawing |
Why the preservative matters
Every time a needle goes through a rubber stopper, there is a small chance of bringing bacteria in. The benzyl alcohol in bacteriostatic water does not sterilize anything, but it holds back bacterial growth between draws. That is why it is the standard diluent for a vial of peptide that will be used over days or weeks. Sterile water has nothing to stop growth once a vial has been opened.
The 28-day rule
US pharmacy standards give most multi-dose vials a beyond-use date of 28 days after the first puncture, unless the manufacturer states a different limit. After that, the vial should be discarded even if liquid remains. Your pharmacy label or the product insert overrides any general rule. The vial supply calculator checks whether a vial will be used up inside the window you set.
Use the diluent your product specifies
Some products must be mixed with a specific diluent, such as sodium chloride 0.9% or a solution packaged with the drug, because the wrong one can damage the molecule or change how it dissolves. When a product comes with instructions, follow them. The amount of water, whichever type, does not change the amount of peptide; it only changes the concentration. The peptide calculator handles the math for any volume.
Frequently asked questions
Can I use sterile water instead of bacteriostatic water?
Sterile water has no preservative and is made for single use. For a vial you will draw from several times, bacteriostatic water is the usual choice, unless your product specifies another diluent.
How long does bacteriostatic water last once opened?
The common limit for multi-dose vials is 28 days after first puncture, unless the manufacturer says otherwise.