BAC Water, short for Bacteriostatic Water for Injection. It is a sterile, multi-dose water containing 0.9% benzyl alcohol as a preservative. It is used to dissolve, dilute, and reconstitute injectable medications like hormones, peptides, and antibiotics, allowing for repeated needle access without contamination. Its use is crucial for the safe mixing of injectable medications and helps prevent bacterial growth after the vial is opened.