What Is Bacteriostatic Water?
Bacteriostatic water is sterile, non-pyrogenic water for injection that contains 0.9% benzyl alcohol as a bacteriostatic preservative. The benzyl alcohol inhibits the growth of common bacterial contaminants, allowing the container to be re-entered multiple times within a defined window — typically up to 28 days after first puncture — without rapid microbial proliferation. In research-supply terms, bacteriostatic water (often abbreviated "BAC water") is the standard multi-dose diluent specification used wherever a sterile aqueous vehicle must remain viable across repeated withdrawals.
It is not the same as sterile water for injection (SWFI), distilled water, or deionized lab-grade water. Each has a different specification and a different appropriate use case. This guide covers what bacteriostatic water is, what it is made of, what formats it ships in, and how research-supply buyers evaluate it. For product detail, see BAC Water Depot's 10 mL vial listing.
How Is Bacteriostatic Water Made?
Production of research-grade bacteriostatic water follows the same general process model that the USP describes for sterile water for injection, with an added preservative step:
- Source water is purified by multi-stage reverse osmosis followed by distillation or equivalent validated purification.
- The water is tested for endotoxin (LAL), conductivity, total organic carbon (TOC), and microbial bioburden.
- 0.9% (9 mg/mL) benzyl alcohol is added as the bacteriostatic agent.
- The bulk solution is sterile-filtered (0.22 µm) and aseptically filled into Type I borosilicate glass vials with butyl-rubber stoppers and aluminum crimp seals.
- Each lot is sampled and tested by independent laboratories for sterility, endotoxin, identity, and preservative content.
- A per-lot Certificate of Analysis (CoA) is generated and retained.
BAC Water Depot manufactures in an ISO 9001:2015 registered US facility and ships every order with a per-lot CoA. See the facility and quality overview for more on the QMS and lot release process.
Key Specifications of Bacteriostatic Water
Buyers evaluating research-grade bacteriostatic water should expect a specification sheet covering at minimum:
- Active vehicle: Water for Injection (WFI quality)
- Preservative: 0.9% benzyl alcohol (9 mg/mL)
- pH range: 4.5 – 7.0
- Endotoxin: < 0.25 EU/mL (LAL)
- Sterility: Passes USP <71>
- Container: Type I borosilicate glass, 10 mL nominal fill
- Closure: Bromobutyl or chlorobutyl stopper, aluminum crimp seal
- Shelf life: 24 months from manufacture (unopened)
- In-use window: Up to 28 days after first puncture, stored 20–25°C
BAC Water Depot publishes these specifications on every product page and ships a CoA referencing the exact lot in your shipment.
Bacteriostatic Water vs. Other Water Preparations
Research buyers frequently confuse adjacent water types. The table below clarifies the boundaries.
| Type | What it is | When to use | Example | |------|-----------|-------------|---------| | Bacteriostatic water | Sterile WFI + 0.9% benzyl alcohol | Multi-dose research applications where the vial is re-entered | BAC Water Depot CAT # BW-10 | | Sterile water for injection (SWFI) | Sterile WFI, no preservative | Single-use research applications, formulations sensitive to benzyl alcohol | USP SWFI single-dose vial | | Distilled water | Water purified by distillation, not sterile | General lab solutions, glassware rinse | Lab-grade distilled | | Deionized (DI) water | Ion-exchanged, not sterile | Buffer prep, instrument feed water | Type II / Type III DI | | Ultrapure (Type I) water | < 18 MΩ·cm, low TOC | HPLC, molecular biology, trace analysis | Milli-Q-equivalent systems |
For a deeper specification comparison, see the companion guide Bacteriostatic Water vs. Sterile Water.
Why the 0.9% Benzyl Alcohol Concentration?
The 0.9% benzyl alcohol concentration is not arbitrary. It is the historical USP-monograph concentration validated across decades of literature as the minimum effective concentration to inhibit a defined panel of bacterial test organisms while remaining low enough to avoid significant interference with most aqueous research formulations. Higher concentrations introduce solvent effects that can alter solubility and protein stability; lower concentrations fail the bacteriostatic challenge.
Benzyl alcohol is bacteriostatic, not bactericidal — it inhibits growth rather than killing organisms outright. This is why bacteriostatic water still has a defined in-use window (28 days) rather than being treated as indefinitely sterile after puncture.
Common Research-Supply Use Cases
Bacteriostatic water shows up in the following typical research-supply contexts:
- Reconstitution of lyophilized research compounds where a multi-dose diluent is preferred over multiple SWFI vials
- Stock-solution preparation for in-vitro assays where the diluent must remain microbially stable across a multi-day protocol
- Animal-research dosing studies (institutional use) where bacteriostatic stability is needed across a dosing window
- Compounded research preparations in academic and industrial laboratory settings
- Reseller stocking for downstream qualified research customers
All product use is for research and laboratory use only — not for human or veterinary use.
How to Evaluate a Bacteriostatic Water Supplier
A defensible procurement decision rests on more than price. Use this checklist:
- Manufacturing location and QMS — confirm US manufacture and ISO 9001:2015 registration
- Per-lot Certificate of Analysis — the CoA should reference your exact lot number
- Third-party testing — independent lab confirmation of sterility, endotoxin, and preservative concentration
- Container specification — Type I borosilicate glass, validated closure system
- Shelf life and lot dating — minimum 18 months of remaining shelf life at receipt
- Documented supply continuity — multi-lot stocking and demonstrated fulfillment reliability
- Return and money-back policy — a clear, written guarantee (BAC Water Depot offers a 30-day money-back guarantee)
For procurement teams, the bulk purchase page details volume tiers and lot-locking options. The documentation checklist goes deeper on what to request before placing an order.
Common Mistakes to Avoid
- Treating bacteriostatic water as interchangeable with sterile water for injection
- Using bacteriostatic water in a research formulation that has known benzyl alcohol incompatibility (some peptides, certain neonatal-model studies)
- Re-entering a vial beyond the 28-day in-use window
- Storing opened vials above 25°C or in direct sunlight (see storage best practices)
- Accepting a supplier that cannot produce a lot-specific CoA on request
- Buying from marketplace listings where the manufacturer cannot be identified
BAC Water Depot Product Formats
BAC Water Depot supplies bacteriostatic water exclusively in the 10 mL Type I borosilicate vial format under CAT # BW-10. Pricing tiers:
- Single vial: $9.99
- 10-pack: $7.49 per vial
- 25-pack: $6.99 per vial
- Bulk (50+ vials): $6.49 and below per vial
All formats ship from the same ISO 9001:2015 facility, with the same per-lot CoA, the same 30-day money-back guarantee, and the same average buyer rating of 4.9 / 5 across 387 verified research orders. Browse the full shop catalog or review the knowledge base for additional product documentation.
Frequently Asked Questions
What is bacteriostatic water used for?
Bacteriostatic water is used in research and laboratory settings as a multi-dose sterile diluent — typically to reconstitute lyophilized research compounds, prepare stock solutions for in-vitro assays, or supply a stable aqueous vehicle across a multi-day protocol. It is for research use only.
Is bacteriostatic water the same as sterile water?
No. Sterile water for injection (SWFI) contains no preservative and is single-use. Bacteriostatic water contains 0.9% benzyl alcohol, which inhibits bacterial growth and permits the vial to be re-entered multiple times within a 28-day window.
How long does bacteriostatic water last after opening?
Industry convention, backed by USP monograph guidance, is 28 days after first puncture when stored at 20–25°C. After 28 days, the remaining contents should be discarded.
What is the shelf life of unopened bacteriostatic water?
BAC Water Depot's 10 mL vials carry a 24-month shelf life from manufacture date, printed on each vial and confirmed on the per-lot CoA.
Can I make bacteriostatic water myself?
No. Manufacturing bacteriostatic water to research-grade specification requires WFI-quality source water, validated 0.22 µm sterile filtration, aseptic fill, and post-fill sterility and endotoxin testing. This is not reproducible at the bench.
Why is bacteriostatic water sold in 10 mL vials?
The 10 mL format aligns with typical multi-dose research workflows and minimizes waste across a 28-day in-use window. See Why 10 mL Vials Are Standard in Research Supply Chains for the full rationale.
Does BAC Water Depot provide documentation?
Yes. Every order ships with a per-lot Certificate of Analysis covering sterility, endotoxin, preservative concentration, and pH. Additional documentation (safety data sheet, facility QMS summary) is available on request.
Where can I buy bacteriostatic water for research?
Bacteriostatic water for qualified research customers is available directly from BAC Water Depot's shop or in volume through the bulk supply page.
About BAC Water Depot: BAC Water Depot supplies research-grade bacteriostatic water to qualified research institutions and laboratory buyers. All products are manufactured in an ISO 9001:2015 registered US facility, third-party tested by three independent laboratories, and shipped with a per-lot Certificate of Analysis. For research and laboratory use only — not for human or veterinary use.
Last reviewed: May 11, 2026
