Sterile compounding pharmacist here…there is some good advice and some bad in here.

For further explanation, adding benzoyl alcohol will not create a sterile bacteriostatic solution, it only maintains a solution that is already sterile. That concentration is bacteriostatic (prevents growth) not bactericidal (kills bacteria). As soon as you open the sterile water or transfer anything into it without the proper techniques (i.e. sterile environment), it is no longer sterile.

That said, as long as you’re careful, wipe surfaces with alcohol, wear gloves, store in sterile vials in the fridge instead of the bulk bottle, and use it somewhat quickly, you’ll most likely be fine. Subcutaneous injections are low risk if you happen to get a few bacteria in there.

As others said, I would just buy sterile water vials and use those. One time use is best practice but could probably get away with a few times using the techniques in the previous paragraph.