BAC Water Guide · First-Timers

What Is Bacteriostatic Water
and Why Does It Matter?

Bacteriostatic water is the only diluent that makes multi-dose peptide vials safe across 30 days. Plain sterile water has no preservative. That single difference determines how long your reconstituted peptide is safe to use.

What It Is

Bacteriostatic Water — The Definition

Bacteriostatic water (BAC water) is sterile water containing 0.9% benzyl alcohol as a bacteriostatic agent. The benzyl alcohol doesn't sterilize the solution — it prevents bacteria from multiplying within it. This distinction matters: if you accidentally contaminate the vial when inserting a needle (which is impossible to entirely avoid across 20–40 draws), the benzyl alcohol slows any bacterial growth to a clinically safe level across the intended use period.

Without benzyl alcohol, each needle insertion into a multi-dose vial creates a contamination risk that compounds across every subsequent draw. This is why sterile water (no preservative) is appropriate for single-use only — use it, discard the vial. BAC water is what makes a peptide vial safe to use repeatedly over a 28–30 day period.

Key Specifications

Benzyl alcohol content: 0.9% · pH: 4.5–7.0 · Storage: room temperature until opened, then refrigerate · Sterile filtered · Available in 10mL, 30mL vials

BAC vs Sterile Water

The Critical Difference

Bacteriostatic water (BAC water)

Contains 0.9% benzyl alcohol. Safe for multi-dose vials. Reconstituted peptide lasts 28–30 days refrigerated. Standard for all peptide reconstitution protocols.

Sterile water for injection (SWFI)

No preservative. Single-use only — use the full reconstituted vial within 24 hours. Safe for one-time use but impractical for multi-dose peptide protocols. Never store a SWFI-reconstituted vial.

Normal saline (0.9% NaCl)

Not for reconstitution. The sodium chloride content can affect peptide solubility and stability. Use BAC water or SWFI only.

Tap water / distilled water

Never. Not sterile, not pH-appropriate, not safe for injection regardless of filtration.

Where to Get It

Sourcing Bacteriostatic Water

Bacteriostatic water is available from research chemical suppliers (the same sources that supply peptides), some compounding pharmacies, and medical supply companies. It's not prescription-required in the United States for personal use. Amazon carries it from medical supply sellers — search "bacteriostatic water 30mL" and filter for medical-grade products with clear labeling of benzyl alcohol content.

Buy 30mL vials when possible. A 30mL vial provides enough BAC water for multiple peptide vials at 2mL each — the most common reconstitution volume for a 5mg peptide vial. Standard pricing is $8–20 per 30mL vial depending on source. Avoid products that don't clearly state the benzyl alcohol concentration (0.9%) on the label.

FAQ

BAC Water Questions

Can I use saline instead of bacteriostatic water?

No. Saline (0.9% sodium chloride) is not appropriate for peptide reconstitution. The salt content can affect peptide stability and solubility. Bacteriostatic water and sterile water for injection are the only appropriate diluents for injectable peptides. BAC water is the standard for multi-dose vials.

How long is bacteriostatic water good for after opening?

An opened BAC water vial is typically good for 28–30 days at room temperature if stored properly (stopper intact, clean injection technique). Once reconstituted with a peptide, the resulting solution is typically stable for 28–30 days refrigerated at 2–8°C. The benzyl alcohol provides the preservation for both the diluent and the reconstituted solution.

What size BAC water vial do I need?

For most peptide reconstitution, you'll add 2mL of BAC water per vial. A 10mL BAC water vial provides 5 reconstitutions at 2mL each. A 30mL vial provides 15 reconstitutions. Buy the size that matches your usage — BAC water has a finite shelf life once opened, so don't overbuy.