Bacteriostatic vs Sterile Water: Which Should You Use?

Both bacteriostatic water and sterile water look identical and are pharmaceutical-grade — but they serve very different purposes. Choosing the wrong one shortens your peptide's usable life from weeks to hours.

The key difference

Sterile water is purified water with nothing else added. It must be used immediately once the vial is pierced because there is no preservative.

Bacteriostatic water is sterile water plus 0.9% benzyl alcohol — a mild preservative that inhibits bacterial growth for around 28 days after first puncture.

When to use bacteriostatic water

• Multi-dose vials of peptides like tirzepatide, retatrutide, semaglutide, BPC-157
• Any reconstitution intended to last more than 24 hours
• All standard peptide protocols

Buy it on our BAC water page.

When sterile water is acceptable

• Single-use injection prepared and used within minutes
• Peptides where benzyl alcohol is contraindicated (rare — check your specific peptide)

Cost difference

The price gap is negligible. A 10 ml vial of bacteriostatic water costs roughly the same as sterile water but gives you 28× the working window. There is rarely a reason to choose sterile water for ongoing reconstitution.

Frequently asked questions

Can I mix the two?

No — once the peptide is reconstituted, do not add additional solvent. The benzyl alcohol concentration is what gives the 28-day shelf life.

Is benzyl alcohol safe at 0.9%?

Pharmaceutical-grade bacteriostatic water has been the global standard solvent for injectables for over 50 years at this concentration.

Do you sell sterile water?

We stock bacteriostatic water as our default solvent. See the product page.

Can I freeze bacteriostatic water?

No. Freezing destroys peptides reconstituted with it and is not necessary — refrigeration is sufficient.