What Is Bac Water? Bacteriostatic Water Explained
Guide · checked 8 October 2026
Direct answer
Bac water (bacteriostatic water) is sterile water for injection with 0.9% benzyl alcohol (9 mg/mL) added as a preservative. The benzyl alcohol slows the growth of bacteria, which is why one vial can be drawn from more than once. Its labelled use is diluting or dissolving other drugs before injection; it is not injected on its own. Direct Bac Water sells it in 3 mL, 10 mL and 30 mL vials and as Hospira 30 mL.
What is in bacteriostatic water?
Two ingredients. The FDA label for Hospira’s Bacteriostatic Water for Injection, USP describes it as “a sterile, nonpyrogenic preparation of water for injection containing 0.9% (9 mg/mL) or 1.1% (11 mg/mL) of benzyl alcohol added as a bacteriostatic preservative”, with a pH of 5.7 (range 4.5 to 7.0). The common strength is 0.9%; Hospira also lists a 1.1% glass vial. “Sterile” means free of living organisms; “nonpyrogenic” means free of the fever-causing substances that bacteria leave behind.
| Base | Water for injection, USP |
|---|---|
| Preservative | Benzyl alcohol, 0.9% (9 mg/mL); 1.1% on one Hospira glass vial |
| pH | 5.7 (4.5 to 7.0) on the Hospira label |
| Container | Multiple-dose vial |
| Labelled storage | 20 to 25 °C (68 to 77 °F), controlled room temperature |
| Label warning | “NOT FOR USE IN NEONATES” |
| Prescription status | “Rx only” on the FDA-listed products |
What does “bacteriostatic” mean?
Bacteriostatic means it stops bacteria multiplying; it does not mean it kills them. That distinction matters. Each time a needle passes through the rubber stopper there is a chance of bringing bacteria in, and the benzyl alcohol keeps any that get in from growing between draws. It does not make a contaminated vial safe again, and its protection has a limit, which is where the 28-day figure for opened vials comes from (see how long bac water lasts).
What is bac water used for?
The Hospira label states its use in one sentence: it “is indicated only for diluting or dissolving drugs for intravenous, intramuscular or subcutaneous injection, according to instructions of the manufacturer of the drug to be administered.” In practice that means it is the liquid added to a powdered drug or peptide to turn it into a solution. Several prescription products that ship as powder name it as their diluent, including Egrifta WR (tesamorelin), Novarel (hCG) and the 4 mg vial of Serostim (somatropin).
Because it is a diluent, the label rules out using it by itself in a vein: “Intravenous administration of Bacteriostatic Water for Injection without a solute may result in hemolysis”, the bursting of red blood cells. Direct Bac Water sells bacteriostatic water for laboratory research and the reconstitution of legal, physician-prescribed medications only.
How is bac water different from sterile water?
Sterile water for injection is the same water with no preservative. Without benzyl alcohol, a vial is single-dose: once opened, the unused portion is thrown away. Bacteriostatic water is made for repeated draws over days or weeks. The full comparison is in bac water vs sterile water.
| Bacteriostatic water | Sterile water for injection | Bacteriostatic saline | |
|---|---|---|---|
| Base | Water | Water | 0.9% sodium chloride |
| Preservative | 0.9% benzyl alcohol | None | 0.9% benzyl alcohol |
| Vial | Multiple-dose | Single-dose | Multiple-dose |
| Used for neonates | No | Yes, the label’s named alternative | No |
Who should not have benzyl alcohol?
The label lists three groups. Benzyl alcohol “has been associated with toxicity in neonates”, so preparations containing it are not used in newborns, and where water is needed for a neonate’s medication, “only preservative-free Sterile Water for Injection should be used”. It is also not used in epidural or spinal procedures, and not for fluid replacement. Some drug labels add further groups; Serostim’s, for example, names known hypersensitivity to benzyl alcohol.
Is bac water a prescription product?
The FDA-listed bacteriostatic water products, Hospira’s included, carry “Rx only” on the label, so pharmacies such as CVS, Walgreens and Walmart dispense them at the counter rather than selling them off the shelf. Direct Bac Water does not ask for a prescription at checkout and sells for research and the reconstitution of legal, prescribed medications. See do you need a prescription for bac water.
What sizes does bac water come in?
Pharmacy and hospital supply is mostly 30 mL multiple-dose vials. Direct Bac Water stocks four:
| Size | Single vial | Per mL | Best for |
|---|---|---|---|
| 3 mL | $6.50 | $2.17 | Small, occasional use |
| 10 mL | $10.50 | $1.05 | The everyday size |
| 30 mL | $18.95 | $0.63 | Lowest cost per mL of the generic sizes |
| Hospira 30 mL | $23.95 | $0.80 | The Hospira-branded 30 mL vial |
Smaller vials cost more per mL but waste less, because each sealed vial starts its own 28-day clock only when it is first opened. More on choosing a size in the shop and on bac water prices.
Where can you buy bac water with published test results?
Direct Bac Water sells US-made bacteriostatic water online and publishes its lab results: a 10 mL sample from lot 260121 measured 0.912% benzyl alcohol against a labelled 0.9%, and pH 7.068 (Chromate, report #38663). Direct Bac Water dispatches orders placed before 1 pm ET, Monday to Friday, the same business day, and every vial carries its 30-Day Quality Guarantee. See the lab test results.
How is bac water stored?
At room temperature. The label gives 20 to 25 °C (68 to 77 °F) and no refrigerated range; the full answer is in does bac water need to be refrigerated. A sealed vial lasts until its printed expiry date. Once punctured, USP chapter <797> gives a multiple-dose vial 28 days unless the manufacturer says otherwise.
Frequently asked questions
What is bac water?
Bac water is short for bacteriostatic water: sterile water for injection with 0.9% benzyl alcohol (9 mg/mL) added as a preservative, supplied in multiple-dose vials.
What is bacteriostatic water used for?
Diluting or dissolving drugs and peptides that are supplied as powder, before injection. Its FDA label says it is indicated only for that, according to the instructions of the drug’s manufacturer.
Is bac water the same as sterile water?
No. Sterile water for injection has no preservative and is single-dose. Bacteriostatic water contains 0.9% benzyl alcohol, so one vial can be drawn from repeatedly.
Why is benzyl alcohol in bac water?
Benzyl alcohol is the bacteriostatic preservative. It slows the growth of bacteria that may enter the vial when the stopper is punctured, which is what allows a multiple-dose vial.
Can you drink bacteriostatic water?
It is not made for drinking. Its labelled use is as a diluent for injectable drugs, and the benzyl alcohol is a preservative, not a drink ingredient.
Where can I buy bac water?
Pharmacies dispense it on prescription. Direct Bac Water sells it online in 3 mL, 10 mL and 30 mL vials and Hospira 30 mL, from $6.50 a vial, shipped the same business day for orders before 1 pm ET.
Standards & sources
- DailyMed: Bacteriostatic Water for Injection, USP (Hospira): description, indications, contraindications, warnings, storage.
- DailyMed labels for Egrifta WR, Novarel and Serostim: named diluents.
- USP General Chapter <797>, Pharmaceutical Compounding: Sterile Preparations: beyond-use date for opened multiple-dose containers.
Related guides
- Does bac water need to be refrigerated?
- How long does bac water last?
- Bac water vs sterile water
- Where to buy bac water