Bacteriostatic water vs sterile water — when does the difference actually matter?

Both are sterile at the point of opening. The difference is what happens afterwards.

Sterile water has no preservative. Once opened it has no ongoing protection.

Bacteriostatic water has benzyl alcohol, which suppresses bacterial growth over time.

So the difference only matters if the container is going to be entered more than once, or held for any length of time after opening. For a genuinely single-use scenario, the preservative isn't doing much.

Where it flips: benzyl alcohol has compatibility limits, so there are cases where sterile water is the correct choice rather than the lazier one.

Evidence tier: established pharmaceutical practice.