BAC Water is sterile, nonpyrogenic water with a small amount of benzyl alcohol added as a preservative — the 'bacteriostatic' part of the name. It is a prepared reagent rather than a single compound, and it is commonly used as a solvent for returning lyophilized reference materials to solution.
Vestrand provides it as a prepared laboratory reagent, released batch by batch with documentation you can retrieve by lot number.
One quiet detail sets it apart from most of the catalog: it is held at controlled room temperature rather than frozen. The amount of preservative also differs slightly between the two container sizes, so the applicable figure depends on which you receive.
For laboratory research use only. Not for human or veterinary use.