The 30 mL vial is the workhorse of high-throughput benches and the most-searched size of bacteriostatic water. It is also the size most often wasted. This page explains both.
The product
Sterile water with 0.9% benzyl alcohol, endotoxins below 0.5 EU/mL, pH 4.5 to 7.0, in a crimped multi-use vial with a flip-off cap, labeled with lot and expiration; filled to roughly 30.5 to 31 mL so that 30 mL can be withdrawn. Sold in 4, 8, 12, 24 and 36 packs.
Why 30 mL is the largest size
The pharmacopeial standard for bacteriostatic water limits containers to 30 mL. The preservative is validated to protect a limited number of entries over a limited period; a larger multi-use container would invite more entries over more time than the validation covers. That is why there is no 50 or 100 mL bacteriostatic water, and why a lab needing large single volumes uses single-use sterile water instead. See USP water grades explained.
The bench it suits
More than about 10 mL drawn in 28 days: 0.35 mL a day or more on average, or 1 mL or more most working days. On such a bench the 30 mL vial is emptied inside the discard window and its low cost per millilitre is fully realized. A bench that draws 1 mL daily uses a vial every four to six weeks; a bench drawing 3 mL daily opens a new vial every ten days and should keep several in stock.
The waste trap
The 30 mL vial has the lowest sticker price per mL, which draws buyers whose benches do not use 30 mL in 28 days. A bench that draws 1 mL a week discards a 30 mL vial with 26 mL in it; the effective price per mL used is seven times the sticker price, and a 3 mL vial would have been cheaper in use. Before defaulting to 30 mL, estimate actual 28-day consumption; the calculators do it in seconds and the reasoning is in choosing a vial size.
Puncture count
A 30 mL vial drawn at 0.5 mL per entry is punctured sixty times. Stoppers are designed for repeated entry, but each puncture cores a trace of rubber and is a contamination opportunity. High-throughput benches that empty a 30 mL vial in two weeks are well inside what the stopper tolerates; benches that reach sixty punctures over a full month should enter at a slight angle, alternate the puncture site within the target area, and inspect the stopper for visible coring. See how vials are sealed and particulate matter.
Sharing a 30 mL vial between benches
Common, and not ideal. A shared vial is carried between workstations, entered by more people with more devices, and no one owns the discard date. If several benches each draw a little, give each its own 3 or 10 mL vial; if one bench draws a lot, give it the 30 mL.
Ordering
For a bench emptying one 30 mL vial a month, a 12-pack is a year of supply and a 36-pack covers three such benches for a year; most labs order quarterly in 12- or 24-packs. Recurring volumes of a case or more per month are quoted through the bulk and wholesale program. Institutional purchasers will find requisition language in buying for institutional labs.
Related: 3 mL vials, 10 mL vials.
All BAC Water Supply products are supplied for laboratory research use only and are not for human or veterinary use.