Bacteriostatic Water Vial Specifications: Borosilicate Glass, Septum, and Crimp Seal Explained
A bacteriostatic water vial is a three-component container-closure system: a Type I borosilicate glass body, a bromobutyl rubber septum, and an aluminum crimp seal. Each component is specified to meet USP container-closure integrity requirements over the labeled shelf life. The glass type controls leaching and pH drift; the septum elastomer determines coring resistance and self-resealing performance; the crimp seal locks the system. The standard BAC Water Depot CAT # BW-10 is a 10 mL Type I borosilicate vial with a 20 mm bromobutyl septum under an aluminum tear-off crimp.
Why Container Specs Matter for Research-Grade Water
The chemistry inside the vial is only as good as the container holding it. Sub-spec containers introduce:
- pH drift from glass leaching
- Particulate ingress from poor closure integrity
- Benzyl alcohol loss via permeation
- Septum coring under repeated puncture
- Microbial ingress through inadequate seal compression
For a 28-day multi-dose research diluent, container performance is not an afterthought. It is a primary specification.
The Glass — Why Type I Borosilicate
USP <660> classifies pharmaceutical glass into four types based on hydrolytic resistance:
| Type | Glass | Hydrolytic Resistance | Typical Use | |---|---|---|---| | Type I | Borosilicate | Highest | Parenteral, injection vials, ampoules | | Type II | Treated soda-lime | High (surface treated) | Some aqueous parenterals | | Type III | Soda-lime | Moderate | Non-parenteral, dry powder | | Type NP | Non-parenteral | Lowest | Oral solid, general lab |
Type I borosilicate is specified for bacteriostatic water because:
- Low alkali content minimizes pH drift over shelf life
- Excellent chemical resistance to benzyl alcohol
- Thermal shock tolerance for autoclaving during manufacture
- Low extractables and leachables profile
A vial fabricated from Type II or III glass would risk pH drift and ion leaching that could destabilize the formulation.
Glass Dimensional Specifications
A standard 10 mL injection vial has consistent industry dimensions:
- Capacity — 10 mL nominal, 13.5–14 mL brim-full
- Overall height — typically 45 mm
- Body diameter — 24 mm
- Neck finish — 20 mm (matches 20 mm closure)
- Glass thickness — uniform sidewall, no thin spots
- Bottom — push-up or flat, no occlusions
Dimensional control is what enables automated filling-line compatibility downstream and consistent crimp performance.
The Septum — Bromobutyl Rubber Specifics
The septum is the access point. It must puncture cleanly, reseal after needle withdrawal, and not leach extractables into the formulation. Bromobutyl rubber is the standard elastomer for bacteriostatic water vials because of:
- Low gas permeability — preserves benzyl alcohol headspace concentration
- Self-resealing after needle withdrawal
- Low extractables profile vs natural rubber or chlorobutyl
- Compatibility with steam sterilization during manufacture
- Coring resistance up to typical multi-puncture counts
Septum thickness is typically 3 mm for a 20 mm finish. The rubber may be coated on the product-contact face with a fluoropolymer film (e.g., Daikyo Flurotec or West FluroTec) for further extractables reduction in sensitive formulations, though uncoated bromobutyl is the standard for bacteriostatic water.
Septum Coring — What It Is and How to Avoid It
Septum coring is the small disc of rubber punched out during needle insertion. A cored fragment can fall into the vial, contaminating the contents and creating particulate. Prevention:
- Use a sharp, unbarbed needle (single-use, never re-used)
- Insert bevel-up at a shallow angle
- Avoid 18-gauge or larger needles on small-volume vials — overkill for bacteriostatic water draws
- Replace needles when noticeable resistance develops
Bromobutyl at 3 mm with adequate Shore A hardness is engineered to resist coring at the puncture counts typical of a 28-day window. See our shelf life article for puncture-count guidance.
The Crimp Seal — Aluminum Tear-Off
The crimp seal locks the septum to the glass neck under compression. Standard construction:
- Aluminum band, color-coded by manufacturer (often plain or printed)
- Center button or tear-off cap exposing the septum for puncture
- Crimp force applied at sealing produces the seal compression
- One-way: once removed, the integrity is broken
The seal is verified for residual seal force during manufacture; insufficient compression results in seal failure detectable by container-closure integrity testing under USP <1207>.
Vial Component Quick-Reference
| Component | Material / Spec | Function | |---|---|---| | Body | Type I borosilicate, 10 mL | Chemical resistance, dimensional stability | | Neck | 20 mm finish | Matches septum / crimp | | Septum | Bromobutyl, 3 mm | Aseptic access, self-resealing | | Crimp seal | Aluminum, tear-off | Closure compression, tamper evidence | | Label | Pressure-sensitive | Identity, lot, expiry |
Container-Closure Integrity Testing
Container-closure integrity (CCI) is tested per USP <1207> by methods such as:
- Helium leak detection
- Vacuum decay
- High-voltage leak detection (HVLD)
- Dye ingress (less common for QC release)
A research-grade manufacturer validates CCI at shelf-life endpoints to confirm the container-closure system maintains microbial and benzyl alcohol integrity through the labeled expiry. CoA documentation should reference CCI status. For CoA detail see /blog/bacteriostatic-water-coa-explained.
Why 10 mL Is the Research Standard
The 10 mL format dominates research-grade bacteriostatic water for practical reasons:
- Fits the 28-day multi-dose window for typical lab usage patterns
- Standard automated filling-line throughput
- Compatible with most syringe and needle gauges
- Affordable per-vial economics
- Accepted by virtually all research SOPs that cite bacteriostatic water
BAC Water Depot's CAT # BW-10 follows this standard. For ongoing research programs, single vials are $9.99, 10-packs run $7.49/vial, 25-packs are $6.99/vial, and bulk pricing starts from $6.49/vial. Browse the product page at /shop/bacteriostatic-water-10ml or full catalog at /shop.
Comparison to Glass Ampoules
Some sterile water products ship in glass ampoules — single-use, snap-neck. Ampoules are not bacteriostatic water vials. Differences:
- Ampoules are single-use; no septum, no multi-dose capability
- Snap-neck creates particulate risk requiring filtration on draw
- Ampoule contents are typically preservative-free Sterile Water for Injection
- Multi-dose research workflows do not use ampoules
The 10 mL septum vial format is what enables the multi-dose use case.
Comparison to Plastic Vials
Plastic vials (typically cyclic olefin copolymer or COP) exist for some pharmaceutical applications. They are not the standard for bacteriostatic water because:
- Higher gas permeability than Type I glass
- Potential leachables from plastic into preserved aqueous solution
- Lower temperature tolerance during sterilization
- Less established compendial track record for this product class
Type I borosilicate remains the default and the specification you should expect.
Manufacturing Process — How a Vial Reaches the Lab
Behind the finished CAT # BW-10 vial sits a manufacturing chain:
- Vials are received, washed, depyrogenated
- Septa and crimps are sterilized
- Bulk bacteriostatic water solution is compounded — WFI plus benzyl alcohol to 0.9%
- Solution is sterile-filtered through 0.22 µm membrane
- Aseptic fill into vials on validated filling line under HEPA laminar flow
- Septum placed, crimp applied
- Visual inspection, leak inspection, label application
- Lot release with sterility, endotoxin, assay, CCI, and particulate testing
- Per-lot CoA generation
- Distribution under controlled-temperature shipping
This entire chain is what an ISO 9001:2015 quality system documents. For supplier vetting see /blog/how-to-evaluate-bacteriostatic-water-vendor and /about.
Common Spec Mistakes Buyers Make
- Accepting "USP glass" without confirming Type I borosilicate
- Skipping confirmation of septum elastomer (bromobutyl vs natural rubber)
- Ignoring crimp seal integrity on receipt inspection
- Tolerating dimensional variation between lots
- Buying vials without lot-specific CoA
- Confusing ampoules with septum vials
- Accepting plastic vials when glass is specified by SOP
Inspection at Receiving
When a shipment arrives, inspect:
- Carton condition and orientation arrows respected
- Crimp seals all intact, no loose caps
- Glass clarity uniform across the lot
- No cracks, no chips, no bubbles in glass
- Labels legible with lot and expiry
- Per-lot CoA present and matching lot numbers
- Septa not discolored or distorted
Any failure should trigger a hold pending vendor follow-up. See /blog/documentation-review-before-ordering for the full QA receiving checklist.
Frequently Asked Questions
What is a Type I borosilicate vial?
Type I borosilicate is the highest hydrolytic-resistance pharmaceutical glass classification under USP <660>. It minimizes ion leaching and pH drift, making it the standard for parenteral and injection-grade products.
What is the septum made of?
Bromobutyl rubber, typically 3 mm thick, sometimes with a fluoropolymer film on the product-contact face. Selected for low extractables, low gas permeability, and self-resealing performance.
Why a 20 mm neck finish?
20 mm is the standard finish for 10 mL injection vials, matching the standard septum and crimp dimensions used industry-wide. Compatibility with filling lines and capping equipment is the driver.
Does the vial come with a tear-off cap?
Yes. An aluminum crimp seal with a tear-off center exposes the septum on first access. Tamper evidence is preserved until removal.
Can the vial be autoclaved?
The empty vial body and septum are sterilized during manufacture. End-user autoclaving of a filled bacteriostatic water vial is not done — it would damage the formulation and is unnecessary.
What needle gauge minimizes coring?
25–27 gauge for small-volume draws on a 20 mm bromobutyl septum is the typical research choice. Larger gauges increase coring risk.
How many times can the septum be punctured?
Multiple punctures within the 28-day window are the design intent. Best practice is to limit cumulative punctures to what your protocol requires and to use fresh sterile needles each time.
Are BAC Water Depot vials Type I borosilicate?
Yes. CAT # BW-10 ships in a 10 mL Type I borosilicate vial with bromobutyl septum and aluminum crimp seal. Container-closure integrity is validated and reported per lot. See /knowledge-base for full documentation.
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
