Preparation
Sterile water vs bacteriostatic water
The two bottles look identical on a shelf. The difference is one ingredient, and it decides how long each stays usable after opening.
The difference is one ingredient
Both are sterile, filtered, pharmaceutical-grade water. Bacteriostatic water has 0.9% benzyl alcohol; sterile water for injection has nothing. One bottle is protected against what happens after puncture; the other is not.
| Sterile water | Bacteriostatic water | |
|---|---|---|
| Preservative | None | 0.9% benzyl alcohol |
| After first puncture | Use and discard — no protection against contamination | Protected against bacterial growth for a limited period (28-day convention) |
| Typical context | Single-use reconstitution | Multi-use vials |
| Works for every peptide? | Generally yes — it is just water | Almost always, but some products specify against preservatives; documentation decides |
The question people actually ask
Most “which one?” questions online are really about a multi-use research vial being drawn from over days or weeks. That is the case the preservative was invented for: without it, every puncture of both the diluent bottle and the peptide vial is an unguarded contamination event. With it, the liquid defends itself for a while.
What no bottle label can tell you is whether benzyl alcohol suits your specific peptide at your specific concentration. That answer exists only where someone tested it — the supplier's documentation. Where documentation is silent, the honest position is that the choice is conventional rather than verified.
Sources
Updated 17 September 2026 · Therapept Editorial · How these guides are built