The main difference is preservative content. Bacteriostatic Water for Injection commonly contains benzyl alcohol; Sterile Water for Injection is preservative-free.
They are not interchangeable by default
A product label may specify one particular diluent and a particular volume. Substitution can affect compatibility, stability, storage, and patient safety.
Single-dose and multi-dose context
CDC notes that single-dose vials typically lack antimicrobial preservative and must not be used for more than one patient. Multi-dose labeling and preservatives do not remove the need for aseptic technique or a new sterile needle and syringe for each access.
Decision rule
Use only the diluent named by the exact product instructions or confirmed by a pharmacist or prescriber. A calculator can compare math but cannot determine compatibility.