What Is Bacteriostatic Water?

Written by Johnathon Anderson, Ph.D., a research scientist, and Associate Professor at the University of California Davis School of Medicine 

Published by: Peptide Systems

What Is Bacteriostatic Water?

Bacteriostatic water is a sterile, non-pyrogenic aqueous solution containing 0.9% benzyl alcohol, a preservative that inhibits bacterial growth. Because of its antimicrobial properties, it is the gold-standard solvent for reconstituting peptides and other lyophilized research materials.

The benzyl alcohol acts as a bacteriostatic agent, meaning it prevents bacteria from proliferating, allowing the solution to remain stable and usable for multiple withdrawals when handled under clean, aseptic conditions.

In peptide research, bacteriostatic water provides:

• Superior sterility after opening

• Extended usability compared to sterile water

• Better stability for delicate peptide structures

Bacteriostatic Water vs. Sterile Water

While both solutions start as sterile water, they differ in preservatives, shelf life, and research applications.

Key takeaway: Sterile water is appropriate for single-use clinical applications, while bacteriostatic water is ideal for reconstituting peptides and multi-withdrawal laboratory applications.

Why Bacteriostatic Water Is Used to Reconstitute Peptides

Peptides are highly sensitive to microbial contamination, pH changes, and degradation after reconstitution. Bacteriostatic water provides three key advantages:

1. Protection Against Microbial Growth

The benzyl alcohol prevents bacteria from proliferating if minimal contamination occurs during handling.

2. Improved Peptide Stability

A stable, bacteriostatic environment reduces the rate of peptide oxidation, hydrolysis, and enzymatic degradation.

3. Consistent Concentration Over Time

Minimizing degradation ensures your peptide solution maintains a uniform concentration, improving experimental reproducibility.

What Is Bacteriostatic Water Used For?

Primary Uses in Research Laboratories:

• Reconstitution of lyophilized peptides

• Dilution of biologically active compounds

• Preparation of multi-dose research solutions

• Maintaining peptide stability during storage

• Storage of reconstituted peptide solutions over several days

Because peptides begin degrading once dissolved, bacteriostatic water helps preserve bioactivity during experimental workflows.

How Bacteriostatic Water Maintains Peptide Stability

Peptide scientists prefer bacteriostatic water because it enhances stability in two ways:

✔ Extended Shelf Life After Reconstitution

The bacteriostatic agent slows microbial growth, allowing safe, multi-use handling.

✔ Reduced Experimental Variability

Stable concentration + reduced contamination = more reproducible assay results.

For sensitive peptides, such as GHRH analogs, growth-modulating peptides, and neuropeptides, this is critical.

Handling and Storage Guidelines

Bacteriostatic water is stable, but proper handling is essential for preserving sterility and preventing contamination.

Aseptic Handling

Always:

• Use sterile needles and syringes

• Avoid touching vial stoppers

• Minimize open-air exposure

• Discard if cloudiness or particulates appear

Storage Before Opening

• Store sealed vials at 20–25°C (68–77°F)

• Keep away from moisture and direct sunlight

• Use original packaging or amber-tinted containers to prevent photodegradation

Storage After Opening

Once opened, bacteriostatic water should be:

• Stored in the refrigerator (2–8°C)

• Kept tightly sealed

• Used within 28 days

Refrigeration slows microbial activity further and increases solution stability—especially important for peptide labs.

Shelf Life and Viability

Unopened Vials

• Typically stable for up to 2 years

• Maintain sterility through expiration if properly stored

Opened Vials

Must be discarded after:

• 28 days (USP guideline for benzyl alcohol–preserved solutions), or

• Immediately if sterility is compromised

Bacteriostatic Water vs. Sterile Water: Scientific Comparison

Sterile Water (SWFI)

• Pure water with no preservatives

• Must be used immediately after opening

• Often used in clinical settings for single-dose medication dilution

• May still contain trace ions or particulates

Bacteriostatic Water

• Contains 0.9% benzyl alcohol

• Suitable for multi-dose use

• Remains sterile longer

• Ideal for peptide reconstitution and short-term storage

Scientific takeaway:

Sterile water is for immediate-use injections; Bacteriostatic water is for peptides and multi-use laboratory applications.

Best Practices for Peptide Reconstitution

To maximize peptide stability and maintain sterility:

1. Use a new sterile syringe to withdraw bacteriostatic water

2. Inject slowly into lyophilized peptide vial

3. Gently swirl—avoid shaking to prevent foaming and peptide denaturation

4. Store reconstituted peptides refrigerated

5. Avoid freeze-thaw cycles (they degrade peptides rapidly)

Laboratory Safety and Regulatory Compliance

Bacteriostatic water is regulated under:

• USP (United States Pharmacopeia) standards

• FDA manufacturing guidelines for sterile solutions

• USP <71> sterility testing

• USP <85> endotoxin testing

It is not intended for intravenous or oral administration unless specifically formulated for such use under medical supervision. For research applications, bacteriostatic water must be handled under aseptic laboratory technique.

Why Peptide Systems Includes Complimentary Bacteriostatic Water

To support reproducible, high-quality research, every Peptide Systems peptide order includes complimentary USP-grade bacteriostatic water for reconstitution.

Our sterile water:

• Meets USP specifications

• Is manufactured in FDA-compliant facilities

• Provides consistent quality for reliable peptide handling

• Supports optimal peptide solubility and stability

This ensures customers can immediately reconstitute peptides under ideal conditions.

Conclusion

Bacteriostatic water is the most reliable and widely used solvent for reconstituting peptides, offering superior sterility, stability, and consistency compared to sterile water. Its 0.9% benzyl alcohol content inhibits bacterial growth, enables multi-dose usage, preserves peptide integrity, and enhances experimental reproducibility.

When paired with aseptic technique and proper storage, bacteriostatic water helps ensure that your peptide experiments are stable, reproducible, and scientifically valid.