bac water is saline, just sterile
saline solution = water with 0.9% nacl
bac water = water with 0.9% nacl and 0.9% benzyl alcohol (sometimes doesnt even contain 0.9% nacl, thats when it hurts upon injecting)
since you wont keep a single GH vial for like 4 weeks there should be no dangers of bacteria forming so saline is okay