Bacteriostatic water

Bacteriostatic water is sterile water with one addition: a small amount of benzyl alcohol (typically 0.9%) as a preservative. That preservative doesn’t kill bacteria outright — it holds them in check, which is what “bacteriostatic” means (static, as in keeping them from multiplying).

That single ingredient is the whole point. Plain sterile water has no defense, so once you pierce the seal and use it, contamination can grow. The preservative in bacteriostatic water lets you go back into the same vial repeatedly over roughly 28 days without it turning into a bacterial soup. Think of it as the difference between an open jug of water and one with just enough of a preservative to stay usable for a month.

This is why it’s the standard liquid for reconstituting peptides, which are typically dosed a little at a time from one vial across many days. You add the bacteriostatic water to the freeze-dried powder, the peptide dissolves, and the preservative keeps the resulting solution safer between draws.

For a concrete example, suppose a vial of BPC-157 or TB-500 arrives as a freeze-dried powder with instructions to use bacteriostatic water. Adding the stated volume under aseptic conditions turns that powder into a liquid that can be measured across more than one draw; that step is called reconstitution. The preservative helps control bacterial growth after the stopper has been pierced, but it cannot sterilize contaminated powder or rescue sloppy handling. The compound’s instructions still decide which diluent to use and how long the mixed vial can be stored.

Two honest notes: the ~28-day window is a guideline, not a guarantee — label the vial with the date you opened it. And bacteriostatic water isn’t recommended for newborns or for very large volumes, where the benzyl alcohol adds up.