Bacteriostatic Water: What It Is and How It Is Used
Bacteriostatic water is sterile water containing 0.9% benzyl alcohol, a preservative that inhibits bacterial growth. This lets a single vial be used for multiple withdrawals — which is why it is the standard diluent for reconstituting research peptides, unlike single-use sterile water for injection.
Bacteriostatic water is a staple supply in any peptide research workflow. It is the diluent used to reconstitute lyophilized peptides into measurable solutions.
What makes it "bacteriostatic"?
Bacteriostatic water is sterile water that contains 0.9% benzyl alcohol. Benzyl alcohol is a preservative that inhibits the growth of bacteria — "bacteriostatic" means it stops bacteria from multiplying. This lets a single vial be used for multiple withdrawals over its usable window without becoming a contamination risk.
Bacteriostatic vs. sterile water
| Bacteriostatic | Sterile (SWFI) | |
|---|---|---|
| Preservative | 0.9% benzyl alcohol | None |
| Withdrawals | Multiple | Single-use |
| Typical window | ~28 days after opening | Discard after one use |
| Best for | Multi-dose reconstitution | Single-use prep |
Reconstitution diluent. USP-grade sterile water with 0.9% benzyl alcohol. $10
How much to use
The volume of bacteriostatic water you add sets the final concentration of your reconstituted peptide. This is where a calculator saves time and prevents measurement errors.
Open the reconstitution calculator →Storage
Store bacteriostatic water at room temperature and use within about 28 days of first opening. Keep the vial sealed and sanitize the stopper before each withdrawal.
Learn more
Read: How to reconstitute peptides →Key takeaways
- Bacteriostatic water = sterile water + 0.9% benzyl alcohol preservative.
- The preservative allows multiple withdrawals from one vial (~28 days).
- Sterile water (SWFI) has no preservative and is single-use.
- The volume added determines the reconstituted peptide concentration.