Bacteriostatic water vs sterile water

Bacteriostatic water vs sterile water at a glance

Both products are made by Hospira, part of Pfizer, and both labels are public, so the comparison can be done from the source documents rather than from forum lore. The table draws on the Hospira label for Bacteriostatic Water for Injection, USP and the Hospira label for Sterile Water for Injection, USP.

What is the difference between bacteriostatic water and sterile water?

One ingredient and one word on the label. Bacteriostatic Water for Injection, USP is water for injection with 0.9% benzyl alcohol "added as a bacteriostatic preservative", in a container the label calls multiple-dose. Sterile Water for Injection, USP is water for injection with nothing added, and Hospira's label says it is "supplied only in single-dose containers".

The preservative is what allows repeated entry. Each time a needle passes through a vial's stopper there is a chance of introducing bacteria; benzyl alcohol keeps any that get in from multiplying, which is what "bacteriostatic" means. Sterile water has no such protection, so its label treats the vial as finished the moment it is opened: "Do not reuse single-dose containers. Discard unused portion." Everything else, including the storage temperature, is the same.

Can I use sterile water instead of bacteriostatic water?

Not as a drop-in substitute. The two are separate FDA-listed products with separate labels, and the difference between them is exactly the property a multi-entry vial depends on. If a research protocol specifies bacteriostatic water, sterile water does not satisfy it, because nothing in a sterile-water vial prevents bacterial growth once the seal is broken.

The reverse is also true. Some protocols specify a preservative-free diluent, and the bacteriostatic label itself points to "preservative-free Sterile Water for Injection" for the one clinical case it excludes. The protocol names the diluent; the buyer's job is to supply the one named. For the common case in peptide research, a lyophilized vial of BPC-157 or GHK-Cu that will be drawn from over days or weeks, that diluent is bacteriostatic water.

What can be substituted for bacteriostatic water?

There is one other preserved diluent in the same family: Bacteriostatic 0.9% Sodium Chloride Injection, USP, which Hospira also makes. Its label describes an isotonic saline solution with "0.9% (9 mg/mL) benzyl alcohol added as a bacteriostatic preservative", supplied in a multiple-dose container (DailyMed). It shares the preservative and the multiple-dose format, but it is saline, not water, and a protocol that calls for one does not call for the other.

Beyond that, nothing substitutes by default. Sterile water is the single-use alternative; bacteriostatic saline is the preserved isotonic alternative; the choice between them is the protocol's, not the buyer's. Astral's guide covers the same ground from the peptide side.

Which is better for peptides, bacteriostatic water or sterile water?

For nearly all peptide research, bacteriostatic water. A lyophilized peptide vial is reconstituted once and then drawn from repeatedly, and that pattern is what a multiple-dose, preserved diluent exists for. The 30 mL Hospira vial is the standard, and the one usually meant when the name is shortened to "bac water".

Sterile water is the right buy only when a protocol uses the entire reconstituted vial at once and discards the remainder, or specifies preservative-free. If you are not sure which case you are in, the protocol says. If the protocol says bacteriostatic water, the Hospira 30 mL vial is the one to order, and our home page on bacteriostatic water for sale explains what to check on its label.

How long does each last once opened?

Sterile water: it does not. The label is unambiguous about discarding the unused portion of a single-dose container. Bacteriostatic water: the Hospira label does not set a beyond-use date after first entry, so the clinical convention applies. The CDC's injection-safety guidance says an opened multi-dose vial "should be dated and discarded within 28 days unless the manufacturer states another date for that opened vial" (CDC).

In practice that means one 30 mL vial of bacteriostatic water, dated on first entry and kept capped at room temperature, covers four weeks of bench work. Unopened, both products keep at 20 to 25°C until the expiration date printed on the vial.

Can you buy bacteriostatic water at a pharmacy?

With a prescription, yes. Both Hospira labels print "Rx only" (the bacteriostatic water label and the sterile water label), so a pharmacy that stocks either one fills it against a prescription rather than selling it over the counter. Research suppliers sell the same vials to laboratories for research use, which is the usual route for a peptide researcher. Our where to buy bacteriostatic water page goes channel by channel.

Which one should you buy?

If you are reconstituting a research peptide, buy bacteriostatic water, buy the Hospira 30 mL multiple-dose vial, and buy it where you buy the peptide. Astral is in a class of its own on all three counts: its Reconstitution Solution is the genuine Hospira vial, it ships from Astral's own inventory in New York, and it sits beside GLP-3 RT (Astral's name for retatrutide) and the rest of a catalog Astral synthesizes and manufactures in the United States, every item sold for laboratory research only. For the reconstitution arithmetic, use Astral's peptide calculator.

Order Reconstitution Solution at Astral →