Bacteriostatic water is sterile water with a small amount of benzyl alcohol added — 0.9%, or 9 mg per mL. That one ingredient is the whole difference. It stops bacteria from growing after the vial is opened, which is why one bottle can be used for multiple draws instead of being thrown out after a single puncture.
What does "bacteriostatic" actually mean?
It means "stops growth" — not "kills." A bacteriostatic solution doesn't sterilize anything. It simply makes it much harder for bacteria to multiply inside the vial.
That's an important distinction. If a needle picks up bacteria on the way in, the preservative slows things down but doesn't undo the contamination. Clean technique still matters. The benzyl alcohol buys you time and safety margin, not immunity.
Bacteriostatic water vs sterile water
These two get mixed up constantly, and the difference changes how you can use a vial.
If you're reconstituting a peptide and drawing from it more than once, plain sterile water leaves the solution with no protection at all. Bacteriostatic water is the version built for that job.
Is "reconstitution solution" the same as bacteriostatic water?
Sometimes — but not always, and the label is the only way to know.
"Reconstitution solution" is a general term. It just means a liquid you use to dissolve a powder. Some products sold under that name are bacteriostatic water. Others are plain sterile water, sterile saline, or water with a different preservative.
Check the ingredient panel for 0.9% benzyl alcohol. If it's there, you have bacteriostatic water regardless of what the front label calls it. If it isn't, treat the vial as single-use.
What is bacteriostatic water used for?
- Dissolving lyophilized compounds. Freeze-dried peptides come as a powder or cake. Adding liquid turns them into something you can measure and draw.
- Multi-dose laboratory work. The preservative allows repeated sterile draws from one vial across the 28-day window.
- General diluent work. Any bench procedure that needs a preserved diluent rather than plain water.
It is not a solvent for every compound. Some sequences — particularly hydrophobic ones — need a different diluent to dissolve properly. We cover those exceptions in which compounds cannot use regular BAC water alone.
How long does it last?
Two different clocks, and people confuse them:
- Unopened: until the expiry date printed on the vial.
- After first puncture: 28 days, dated from the day you open it.
The full reasoning — including what the 28-day figure is actually based on — is in How Long Is BAC Water Good For? 28-Day Rule vs Reality.
How should you store it?
Room temperature, roughly 20–25°C, out of direct light, never frozen. Refrigeration after opening is acceptable and common, but it isn't required. The one hard rule is the 28-day clock. Details: Do You Need to Refrigerate BAC Water?
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Shop Bacteriostatic Water →Frequently Asked Questions
Does bacteriostatic water expire?
Yes. The vial carries a manufacturer expiry date, and once you puncture the stopper the usable window drops to 28 days no matter what the printed date says. Write the date on the vial when you first open it.
Can you freeze bacteriostatic water?
No. Freezing can damage the container and affect the solution. Keep it above freezing and away from direct light.
Does bacteriostatic water sterilize a contaminated vial?
No. It inhibits bacterial growth; it doesn't sterilize. A contaminated needle or a dirty septum still spoils the contents.
Is bacteriostatic water the same as saline?
No. Saline is salt water, and most saline has no preservative. Bacteriostatic saline exists and does contain benzyl alcohol, but plain saline should be treated as single-use.
How much do I add to a peptide vial?
That depends on the concentration you want, not the dose. Our guide on how much bacteriostatic water to add walks through the maths, and the Peptide Calculator handles syringe units for you.
References & Standards
- Bacteriostatic Water for Injection, USP — FDA/DailyMed Label Reference
- CDC Safe Injection & Multi-Dose Medication Handling Guidelines
Bacteriostatic water is sterile water plus 0.9% benzyl alcohol — a preservative that lets a vial be used more than once. Match it to the job, date it when you open it, and store it away from light.
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