Bacteriostatic Water
Bacteriostatic water is sterile water containing 0.9% benzyl alcohol as a preservative. It's the standard mixing solution for reconstituting peptides in research applications.
What is Bacteriostatic Water?
Bacteriostatic water (BAC water) is sterile water for injection that contains 0.9% benzyl alcohol as a preservative. The benzyl alcohol prevents bacterial growth, making it suitable for multiple-use applications. This makes it the preferred choice for peptide reconstitution in research settings.
Unlike sterile water for injection (which contains no preservatives), bacteriostatic water remains sterile for multiple withdrawals from the same vial when proper aseptic technique is maintained.
Why Bacteriostatic Water Matters for Peptides
Most research peptides arrive as lyophilised (freeze-dried) powders that require reconstitution before use. The choice of mixing solution directly affects:
- Peptide stability: Some peptides are sensitive to pH changes
- Storage life: Preserved solutions last longer once reconstituted
- Research consistency: Standardised reconstitution improves reproducibility
- Contamination risk: The preservative provides protection against bacterial growth
Advantages Over Alternatives
- Sterile water: No preservative means single-use only
- Saline: May interact with certain peptides
- Buffer solutions: Often unnecessary and may complicate research
How Bacteriostatic Water is Used
The reconstitution process involves drawing the appropriate volume of BAC water into a syringe and slowly injecting it down the side of the peptide vial. Never inject directly onto the powder, as this can damage delicate peptide structures.
Typical Usage Volumes
- 2mg peptide vial: 1-2ml BAC water
- 5mg peptide vial: 2-5ml BAC water
- 10mg peptide vial: 2-10ml BAC water
Use our reconstitution calculator to determine exact volumes for your desired concentration.
Storage and Handling
Unopened vials should be stored at room temperature away from direct light. Once opened, store in the refrigerator and use within 28 days. Always use proper aseptic technique when withdrawing solutions.
UK Availability Context
In the UK, bacteriostatic water is available through research suppliers and some online retailers. It's regulated as a research chemical rather than a medicinal product, making it accessible for legitimate research purposes.
When sourcing BAC water in the UK, ensure suppliers provide:
- Certificate of analysis
- Proper sterile packaging
- Clear labelling with concentration
- Appropriate storage guidance
Check our supplies hub for current UK supplier recommendations and our peptide storage guide for best practices.
What the numbers mean
Understanding Bacteriostatic Water Labels
Concentration
- 0.9% benzyl alcohol: This is the standard preservative concentration - enough to prevent bacterial growth without affecting most peptides
- Sterile Water for Injection USP: Indicates pharmaceutical-grade water meeting strict purity standards
Volume Sizes
- 10ml vials: Most common size, suitable for multiple reconstitutions
- 30ml vials: Bulk size for frequent users
- 3ml vials: Smaller option for occasional use
Labelling Terms
- Multiple-dose: Can be used repeatedly over 28 days when stored properly
- For injection: Pharmaceutical grade suitable for research applications
- Preservative-free: This would be sterile water, not bacteriostatic water
- Isotonic: Some products may mention this, referring to salt content matching body fluids
Storage Instructions
- Room temperature: Unopened vials stable at 15-25°C
- Refrigerate after opening: 2-8°C extends useable life
- Use within 28 days: Standard timeframe once seal is broken
How to choose
Choosing Bacteriostatic Water in the UK
Essential Requirements
Look for pharmaceutical-grade water from reputable suppliers. The product must contain exactly 0.9% benzyl alcohol - higher concentrations may damage peptides, whilst lower concentrations won't provide adequate preservation.
Quality Indicators
- Certificate of analysis from batch testing
- Clear, colourless solution
- Proper sterile packaging (crimped vial tops)
- Professional labelling with lot numbers
- UK or EU manufacturing preferred
Volume Selection
Choose based on your research frequency:
- Occasional use: 10ml vials
- Regular research: 30ml vials offer better value
- Bulk users: Consider multiple 10ml vials for freshness
Red Flags to Avoid
- Unclear preservative concentrations
- No certificate of analysis
- Damaged or poorly sealed vials
- Extremely low prices (suggests poor quality)
- Non-pharmaceutical suppliers
- Products with additional additives
Quick Selection Checklist
- 0.9% benzyl alcohol concentration confirmed
- Pharmaceutical grade (USP/Ph.Eur standard)
- Certificate of analysis available
- Proper sterile packaging
- UK/EU supplier with good reputation
- Appropriate volume for usage
- Clear expiry dates
- Reasonable pricing (not suspiciously cheap)
Top picks
We've reviewed the best bacteriostatic water available in the UK.
Best Places to Buy Bacteriostatic Water in the UK (2026) →Frequently asked questions
Can I use regular sterile water instead of bacteriostatic water?
You can use sterile water for injection, but it lacks preservatives so must be discarded after single use. Bacteriostatic water allows multiple withdrawals over 28 days when stored properly, making it more practical and cost-effective for research applications.
How long does bacteriostatic water last once opened?
Once opened, bacteriostatic water should be used within 28 days when stored in the refrigerator at 2-8°C. Always maintain sterile technique when withdrawing solutions. Unopened vials can be stored at room temperature until their expiry date.
Is bacteriostatic water legal to buy in the UK?
Yes, bacteriostatic water is legal to purchase in the UK for research purposes. It's classified as a research chemical rather than a medicine. Reputable suppliers will require confirmation of research intent and may have age restrictions.
What's the difference between 0.9% and other concentrations?
The 0.9% benzyl alcohol concentration is the pharmaceutical standard that provides effective preservation without damaging most peptides. Higher concentrations may harm sensitive peptides, whilst lower concentrations won't adequately prevent bacterial growth.
Can I make my own bacteriostatic water?
Making bacteriostatic water at home isn't recommended. Achieving sterility and precise 0.9% benzyl alcohol concentration requires pharmaceutical equipment and quality control. Commercial products from reputable suppliers ensure sterility and consistent concentration.
Should I refrigerate unopened bacteriostatic water?
No, unopened bacteriostatic water should be stored at room temperature (15-25°C) away from direct light. Only refrigerate after opening. Storing unopened vials in the fridge may cause temperature fluctuations when removed for use.
What size vial should I buy for peptide research?
For beginners, 10ml vials are ideal - enough for multiple reconstitutions without waste. If you're conducting regular research with multiple peptides, 30ml vials offer better value. Avoid very large volumes unless you're certain of usage frequency.
Can bacteriostatic water go off or become contaminated?
Yes, if stored improperly or used beyond 28 days after opening, bacterial contamination can occur. Signs include cloudiness, particles, or unusual odour. Always use sterile technique, refrigerate after opening, and discard after the recommended timeframe.