What is bacteriostatic water?
Bacteriostatic water, often called BAC water, is sterile water containing a bacteriostatic preservative. It is commonly discussed with multi-dose vials, but it is not automatically correct for every product.
Key takeaways
- BAC water contains a preservative; sterile water for injection does not.
- Diluent choice can affect handling, shelf life, and suitability for a specific product.
- Use the diluent specified by the label, pharmacy, or clinician.
BAC water vs sterile water
The practical difference is the preservative. BAC water includes a bacteriostatic agent, commonly benzyl alcohol, which helps inhibit bacterial growth after the vial is accessed.
Sterile water for injection is sterile when unopened, but it does not contain the same preservative. That can make its use window different once opened.
Why the choice matters
Peptide users often focus only on the calculator math, but the diluent is part of the protocol. The same vial mixed with the same volume will produce the same concentration, but handling and beyond-use instructions may differ.
- Check whether the product requires a specific diluent
- Do not substitute diluents when instructions are explicit
- Label opened and reconstituted vials with dates
How BAC water affects the calculator
For math, the key input is the volume added. Whether you add 1 mL, 2 mL, or 3 mL changes the concentration and the amount to draw.
The calculator does not decide which diluent is medically appropriate; it converts the setup you enter into dose volume and syringe units.