Bacteriostatic Water vs Sterile Water: What's the Difference?
The difference is the preservative. Bacteriostatic water is sterile water for injection plus 0.9% (9 mg/mL) benzyl alcohol, so a multiple-dose vial can be entered more than once. Sterile water for injection has no preservative and is supplied in single-dose containers. Both are labeled only for diluting or dissolving drugs, not for injecting on their own.
Bacteriostatic Water vs Sterile Water for Injection
Same base, same labeled purpose, one deciding ingredient. Every row below comes from Hospira's labeling for Bacteriostatic Water for Injection, USP and Sterile Water for Injection, USP.
| Feature | Bacteriostatic Water | Sterile Water for Injection |
|---|---|---|
| Sterile and nonpyrogenic | Yes | Yes |
| Preservative | 0.9% (9 mg/mL) benzyl alcohol | None (no bacteriostat or antimicrobial agent) |
| Container | Multiple-dose vial | Single-dose vial |
| Re-entry | Repeated withdrawals, aseptic technique | Do not reuse the container |
| Labeled use | Diluting or dissolving drugs for injection | Diluting or dissolving drugs for injection |
| Injected on its own | No | No (hemolysis risk without a solute) |
| Neonates | Not for use | The label's choice for neonates |
| Storage (unopened) | 20°C to 25°C (68°F to 77°F) | 20°C to 25°C (68°F to 77°F) |
The deciding difference is the preservative, and everything else follows from it.
What is bacteriostatic water?
Bacteriostatic water is sterile water for injection with a preservative added. Hospira’s Bacteriostatic Water for Injection, USP contains 0.9% (9 mg/mL) benzyl alcohol as a bacteriostatic preservative, with a pH of 5.7 (4.5 to 7.0). “Bacteriostatic” means it stops bacteria from multiplying. It does not sterilize anything that is already contaminated.
The label says 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.” It comes in a multiple-dose container, so repeated withdrawals are allowed with aseptic technique. The Hospira 30 mL plastic fliptop vial is NDC 0409-3977-01, and a tray of 25 is NDC 0409-3977-03.
What is sterile water for injection?
Sterile Water for Injection, USP is water with nothing added. Hospira’s label says it “contains no bacteriostat, antimicrobial agent or added buffer,” and that it is “supplied only in single-dose containers to dilute or dissolve drugs for injection.” The label also says: “Do not reuse single-dose containers.”
Its labeled purpose is the same as bacteriostatic water: diluting or dissolving drugs. With no preservative in the vial, it is packaged for one use.
The differences that matter
1. The preservative
Bacteriostatic water has 0.9% benzyl alcohol. Sterile water has none. Note that “0.9%” is a concentration of benzyl alcohol here, not the 0.9% sodium chloride in normal saline.
2. Multiple-dose vs single-dose
The preservative is what lets a bacteriostatic water vial be entered more than once. Sterile water carries no such protection, so its container is single-dose and is not reused.
3. Newborns
Hospira’s bacteriostatic water label says “NOT FOR USE IN NEONATES.” It states that benzyl alcohol “has been associated with toxicity in neonates” and that where water is needed to prepare or dilute medications for neonates, “only preservative-free Sterile Water for Injection should be used.”
4. Neither is for injecting on its own
Both labels limit the product to diluting or dissolving drugs. The sterile water label warns that “intravenous administration of Sterile Water for Injection without a solute may result in hemolysis,” meaning damage to red blood cells, and both labels say the water must be made approximately isotonic before use.
What they share
Both are sterile and nonpyrogenic, both are labeled to be stored at 20°C to 25°C (68°F to 77°F), and both are meant to be used the way the drug’s maker directs.
Can you use sterile water instead of bacteriostatic water?
Neither water is a free swap. Both labels point to the same rule: use the diluent as the drug’s maker directs. So the question to answer is what the instructions for the product you are mixing say.
- The instructions name bacteriostatic water: use bacteriostatic water. Multiple entries are allowed with aseptic technique.
- The instructions name sterile water for injection: use sterile water, and treat the vial as single-use.
- The patient is a newborn: the label allows only preservative-free sterile water.
- The instructions don’t say: ask a pharmacist or prescriber. Don’t guess.
One practical consequence: a sterile water container has no preservative, so it is not meant to be drawn from repeatedly. Once the water is mixed with a drug, the storage instructions for that mixed product apply.
Other liquids are not substitutes either. Bacteriostatic saline (0.9% sodium chloride with benzyl alcohol) and normal saline are different products, and water sold for other uses, such as distilled water for appliances, is not labeled sterile or for injection.
How long does each last once opened?
Bacteriostatic water: the Hospira label allows repeated withdrawals but sets no discard period. The common limit of 28 days for an opened multiple-dose vial comes from USP General Chapter <797> and CDC infection-control guidance (unless the manufacturer states otherwise), and the Joint Commission applies it. Write the date you first opened the vial on it. An unopened vial is good until the expiration date printed on it.
Sterile water for injection: single-dose. Discard what is left after use.
For either, don’t use it if the liquid is cloudy, has particles, the seal is damaged or the expiration date has passed.
How to tell which one you are holding
Read the printed label on the vial. Don’t go by the cap or the carton color.
- Bacteriostatic: “Bacteriostatic Water for Injection, USP,” 0.9% benzyl alcohol (9 mg/mL), “multiple-dose,” and “Not for use in neonates.”
- Sterile: “Sterile Water for Injection, USP,” “single-dose,” and no preservative listed.
The Hospira bacteriostatic water 30 mL vial is NDC 0409-3977-01. If a vial in front of you doesn’t match its label, don’t use it.
Bacteriostatic vs Sterile Water FAQ
Is bacteriostatic water the same as sterile water?
No. Bacteriostatic water is sterile water with 0.9% benzyl alcohol added as a preservative and comes in multiple-dose vials. Sterile water for injection has no preservative and comes in single-dose containers. Both are labeled only for diluting or dissolving drugs.
Can I use sterile water instead of bacteriostatic water?
Only if the instructions for the drug you are mixing allow it. The label says to use the diluent as the drug's maker directs. Treat sterile water as single-use, because it has no preservative. If the instructions don't say, ask a pharmacist or prescriber.
Is water for injection the same as sterile water?
Nearly. Water for Injection is the pharmacopeial grade of water. Sterile Water for Injection is that water packaged and sterilized in a container. Bacteriostatic Water for Injection is the same water with benzyl alcohol added.
Can you use sterile water for peptide reconstitution?
Peptide products come with the maker's instructions, and some name bacteriostatic water while others name sterile water. Follow those instructions. We sell the water and don't give mixing or dosing advice. If a product calls for sterile water, remember its container is single-use.
What is the difference between normal saline and bacteriostatic water?
Normal saline is 0.9% sodium chloride in water, so it contains salt. Bacteriostatic water is water with 0.9% benzyl alcohol and no salt. The matching 0.9% refers to different substances. Bacteriostatic sodium chloride is a separate product that has both.
Is bacteriostatic water safe for newborns?
No. Hospira's label says "NOT FOR USE IN NEONATES" because benzyl alcohol has been associated with toxicity in neonates. For medications used in neonates, the label says to use only preservative-free Sterile Water for Injection.
How long is bacteriostatic water good for after opening?
The Hospira label sets no number. Standard practice for an opened multiple-dose vial is 28 days, from USP <797> and CDC guidance unless the manufacturer says otherwise. Date the vial when you first open it. Unopened, it is good until the printed expiration date.
Ask about the label or your order. A real person answers.
Contact usSources and how we checked
- Hospira Bacteriostatic Water for Injection, USP: Pfizer prescribing information
- Hospira Sterile Water for Injection, USP: Pfizer prescribing information
- USP General Chapter <797>, CDC injection-safety guidance and Joint Commission multi-dose vial guidance, for the 28-day opened-vial practice (not a label statement)
Label quotes and NDC numbers were checked against the Pfizer labeling pages on 2026-10-20. Labels change, so check the current label for the exact vial in your hands. Hospira Bac Water is an independent seller, and Hospira is a registered trademark of Pfizer Inc.