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Basics & Technique

BAC water vs sterile water vs saline - which one do I buy?

Updated 2026-05-02

Buy BAC water. That's bacteriostatic water for injection, with a tiny amount of preservative (benzyl alcohol 0.9%). It's what almost every peptide uses, and it keeps your mixed vial safe for 28 days in the fridge. Sterile water works but has no preservative - it's single-use, 24 to 48 hours. Saline is not the right product for peptides; it has salt in it and can mess up how the peptide holds together.

IfIf you're mixing BPC-157, TB-500, CJC-1295, ipamorelin, or most GLP-1s
Thenthen use BAC water
IfIf you're mixing Melanotan II or PT-141
Thenthen use 0.6% acetic acid water - BAC water will not dissolve these properly
IfIf all you have is sterile water
Thenthen mix only one dose and discard the rest
IfIf someone tells you to use saline
Thenthen don't
Key facts
  • BAC water: 0.9% benzyl alcohol preservative, 28 days multi-dose, USP standard for multi-dose injectables
  • Sterile water for injection (SWFI): no preservative, single-dose, 24 to 48 hour window
  • Saline (0.9% NaCl): for IV and wound irrigation, not peptide reconstitution - can cause aggregation or salt instability
  • Benzyl alcohol disrupts bacterial cell membranes and does not affect peptide structure at 0.9%
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