Bacteriostatic water for injection, USP is sterile water carrying benzyl alcohol as a bacteriostatic preservative, supplied in a multiple-dose glass vial. The preservative is what allows the septum to be entered repeatedly instead of once, which is why it is the standard diluent for reconstituting lyophilized research material on the bench.
What the preservative actually does
Benzyl alcohol suppresses microbial growth in the vial between entries. It does not sterilise anything, and it does not make an entered vial permanently safe. What it buys is a working window across multiple withdrawals rather than a single-use container that must be discarded the moment it is opened. The exact concentration is printed on the vial label along with the lot number and expiry date.
That single property drives the whole workflow. A 30 ml multiple-dose vial can reconstitute many cartridges over weeks, where an equivalent volume of single-use sterile water would be discarded after the first draw.
Bacteriostatic water compared with sterile water
Sterile water for injection carries no preservative. It is a single-entry container: correct where a preservative would interfere with the material, and wasteful where it would not. Bacteriostatic water is the multiple-entry option and is what most bench reconstitution work uses.
When not to reach for bacteriostatic water: if the compound or the protocol is known to be incompatible with benzyl alcohol, the preservative is a variable you did not intend to introduce, and preservative-free sterile water is the correct diluent instead. We stock the bacteriostatic form because it fits the majority of reconstitution work, but the majority is not all of it, and choosing the diluent is part of designing the preparation rather than something the hardware decides for you.
The 28-day convention
Standard multiple-dose practice is to discard the vial 28 days after the first septum puncture, and to date the vial at that first entry rather than trying to remember later. The count runs from first entry, not from opening the carton and not from the expiry date printed on the label. Those are three different dates and conflating them is the usual error.
Storage
Store at controlled room temperature, 68 to 77 degrees Fahrenheit (20 to 25 degrees Celsius), away from direct sunlight. Do not freeze. Brief ambient swings in transit do not compromise integrity, but prolonged freezing or heat after delivery will, and temperature exposure after a package leaves our facility is outside our control. Inspect every vial before use: the solution should be clear and free of particulates, and the seal intact.
How much to buy
Bacteriostatic water is stocked as a single 30 ml vial, in multi-vial bundles, and as a factory-sealed case, with the cost per vial falling as the bundle grows. The live options are in the variant picker on the product page.
Buying deep only helps if the vials get used inside their shelf life. A sealed case that outlives its expiry date is more expensive than single vials bought as needed, so scale the order to the actual pace of work rather than to the per-vial figure.
Specifications
| Product | Bacteriostatic water for injection, USP |
|---|---|
| Preservative | Benzyl alcohol, as printed on the vial label |
| Vial | 30 ml multiple-dose glass vial with rubber septum |
| Entries | Multiple, which is what the preservative permits |
| Storage | Controlled room temperature, 68 to 77 degrees Fahrenheit (20 to 25 degrees Celsius). Do not freeze |
| After first entry | Discard 28 days after the first septum puncture |
| Traceability | Lot number and expiry date printed on every vial |
| Intended use | Research, educational, and demonstration use only |
Pairs with: the 3 ml glass cartridges you are filling and any pen from the research pens collection. If a vial has to travel, the travel coolers hold temperature and display it.
Common questions
What is bacteriostatic water for injection?
Sterile water containing benzyl alcohol as a bacteriostatic preservative, supplied in a multiple-dose vial. The preservative suppresses microbial growth between entries, which is what allows the same vial to be used across repeated withdrawals.
How is it different from sterile water for injection?
Sterile water has no preservative and is a single-entry container. Bacteriostatic water can be entered repeatedly. Where a protocol is incompatible with benzyl alcohol, preservative-free sterile water is the correct choice instead.
How long does a vial last once it has been entered?
The standard multiple-dose convention is to discard it 28 days after the first septum puncture. Date the vial at first entry; that count is separate from the expiry date printed on the label.
How should it be stored?
At controlled room temperature, 68 to 77 degrees Fahrenheit (20 to 25 degrees Celsius), out of direct sunlight. Do not freeze.
How much do I need?
It depends entirely on how many cartridges you prepare and at what concentration. Vials are stocked singly, in bundles and as a sealed case; the variant picker on the product page carries the live sizes. Buy to the pace of the work rather than to the per-vial cost, because unused vials expire.
Is this for human use?
No. It is supplied for research, educational, and demonstration use only, and not for human or veterinary use or for any diagnostic or therapeutic procedure.
From The Lab
Everything in this collection is sold for research, educational, and demonstration use only. Nothing here is a medical device, nothing is sold sterile, and nothing is for human or veterinary use of any kind. Not evaluated by the FDA. Nothing on this page is dosing guidance. 21+.
