Bacteriostatic water (often labeled "BAC water") is sterile water for injection that contains a small amount of a bacteriostatic agent, typically benzyl alcohol.

It is supplied as a diluent to reconstitute compatible medications and is not a therapeutic agent by itself.

The bacteriostatic component inhibits growth of certain bacteria in the solution, allowing limited multi-dose use from a single vial under appropriate sterile conditions.

BAC water is used to dissolve or dilute medications that are specifically labeled as compatible with bacteriostatic diluents.

Some products require preservative-free sterile water instead; matching the correct diluent to the product label is essential.

BAC water is not appropriate for all patient populations (for example, neonates may require preservative-free preparations). Product labeling and local policy provide detailed guidance.

BAC water does not have a dose in the therapeutic sense; the volume used is determined by the medication being reconstituted and the instructions in that medication’s labeling.

This page does not provide mixing or administration instructions for any specific drug.

BAC water is packaged in multi-dose vials of varying volumes. It is used in combination with injectable medications that explicitly allow a bacteriostatic diluent.

BAC water is a well-established pharmaceutical excipient; safety and compatibility considerations are addressed in pharmacopeial standards and product-specific labeling rather than in traditional clinical trials.

Future FAQs may clarify when bacteriostatic versus preservative-free diluents are appropriate, how long reconstituted products can be stored, and what questions to ask a pharmacist or clinician about mixing injectable medications. Answers will remain educational and non-prescriptive.