Side by side
What each product's US label says, from the two labels cited below.
| Property | Bacteriostatic water | Sterile water for injection |
|---|---|---|
| Preservative | Benzyl alcohol, 0.9% (9 mg/mL) or 1.1% (11 mg/mL)[1] | None: no antimicrobial agent or other preservative[2] |
| Container | Multiple-dose, for repeated withdrawals[1] | Single-dose vial[2] |
| After the first draw | Further draws allowed; see how long below | Discard the unused amount immediately[2] |
| Label storage | 20 to 25 °C[1] | 20 to 25 °C[2] |
The Primara Labs BAC Water listing describes it as: 3 ml sterile vial, 0.9% benzyl alcohol.
What the benzyl alcohol does
The Hospira label describes the benzyl alcohol as a bacteriostatic preservative[1]. Bacteriostatic means it holds back the growth of bacteria rather than sterilising the solution: it limits what a few organisms carried in on a needle can grow into between draws. It does not make a contaminated vial clean, so it is no substitute for alcohol on the stopper and a new syringe for every entry. The same label warns that benzyl alcohol is not for use in neonates, one of several warnings it carries.
Why multi-draw vials use BAC water
Every time a needle goes through a stopper there is a chance of carrying microbes into the vial. A reconstituted peptide vial is usually drawn from several times, so the diluent needs something working against growth between those draws. Sterile water has nothing added, and its label treats it as single-dose, discarding what is left after the first withdrawal[2]. Bacteriostatic water is made for repeated withdrawals from one container[1], and a peptide dissolved in it carries that preservative with it.
How long an opened vial is used
The Hospira bacteriostatic water label gives no in-use period. CDC guidance, citing USP chapter 797, is that an opened multi-dose vial is dated and discarded within 28 days unless the manufacturer states another date, and never used past its original expiry[3]. The US instructions for tesamorelin, a peptide medicine supplied with bacteriostatic water, say to throw away the water left in the bottle 28 days after first use[4]. Write the opening date on the water vial the first time it is pierced. For a reconstituted peptide, the peptide's own stability sets the window: follow the lab report or product label. The storage guide covers the rest.
Supplied for laboratory research use only. Not for human consumption. Nothing on this page is medical advice, and nothing here suggests an amount, a frequency or a protocol for any compound.