Bacteriostatic water is sold in exactly three vial sizes: 3 mL, 10 mL and 30 mL. The right one for a given bench is not the cheapest per millilitre; it is the one that will actually be used up inside the 28-day window after first puncture. This guide explains why the sizes are what they are and how to choose between them.
Why 30 mL is the largest vial
The pharmacopeial standard for bacteriostatic water limits the container to 30 mL. The reasoning is straightforward: the preservative is validated to protect a multi-use vial through a limited number of entries over a limited period, and a larger container would invite more entries over a longer time. That is why bacteriostatic water is never sold in 100 mL or 500 mL bottles the way sterile water is. If a workflow needs that much sterile water at once, a single-use bottle of preservative-free sterile water is the correct product; see bacteriostatic water vs. sterile water.
The three sizes at a glance
| 3 mL | 10 mL | 30 mL | |
|---|---|---|---|
| Best for | Low-volume benches, occasional use, many workstations | Moderate, regular use | High-throughput benches, daily use |
| Typical use inside 28 days | Up to about 0.1 mL per day | About 0.1 to 0.35 mL per day | More than about 0.35 mL per day (1 mL or more per day is common) |
| Cost per mL | Highest | Middle | Lowest |
| Waste risk if underused | Lowest | Moderate | Highest |
| Stopper punctures per vial | Few | Moderate | Many |
Start from the 28-day rule, not the price tag
Once a vial is punctured, the common laboratory convention is to discard it at 28 days regardless of what remains (see storage and shelf life). So the question to ask is: how many millilitres will this bench draw from one vial in four weeks?
- A bench that draws 0.5 mL twice a week uses about 4 mL a month. A 3 mL vial will run out slightly early; a 10 mL vial will be discarded two-thirds full. Two 3 mL vials, or one 10 mL vial for a bench that will use a little more, are both reasonable.
- A bench that draws 1 mL every working day uses roughly 20 mL a month. A 30 mL vial is used up with a little margin; a 10 mL vial would need replacing every two weeks.
- A bench that draws 2 to 3 mL a day will empty a 30 mL vial in two weeks and should keep several on hand.
Effective cost per millilitre
The list price divided by the vial volume gives the nominal cost per mL, and by that measure 30 mL vials always win. The number that matters is the price divided by the volume actually used before discard. A 30 mL vial thrown away with 20 mL left has cost three times its nominal per-mL price. Run the calculation for each bench using its real consumption and the answer often changes.
Stopper wear and contamination risk
Every entry through a rubber stopper cores a minute amount of material and creates a track that can leak or harbor organisms. A 30 mL vial drawn at 0.5 mL per entry receives sixty punctures over its life; a 3 mL vial receives six. Where the withdrawal volume is small, smaller vials mean fewer punctures per stopper and a shorter exposure window for each vial, which is why many quality-focused laboratories deliberately choose 3 mL or 10 mL vials for low-volume work even when 30 mL vials are cheaper per mL.
Multiple workstations and lot control
When several workstations each need their own vial, small vials keep each station on its own sealed supply rather than passing one 30 mL vial around the room. Small vials also make lot segregation simpler: when a project must be run on a single lot, a tray of 3 mL or 10 mL vials from one lot can be dedicated to it without opening a large volume that other work will consume.
Pack sizes
BAC Water Supply sells each vial size in packs of 4, 8, 12, 24 and 36. A useful way to size an order is to estimate monthly vial consumption per bench, multiply by the number of benches, and buy two to three months of stock at a time so that every vial is well inside its expiration date when it is opened. Larger recurring volumes are handled through our bulk and wholesale program.
Quick decision guide
- Estimate millilitres drawn per bench per 28 days.
- Under 3 mL: choose 3 mL vials. 3 to 10 mL: choose 10 mL. Over 10 mL: choose 30 mL.
- If withdrawals are very small (0.1 to 0.2 mL) or many people share the vial, step down one size to limit punctures per stopper.
- If a project needs single-lot supply, buy that project its own pack.
All three sizes are the same product: sterile water with 0.9% benzyl alcohol in a sealed multi-use vial. Browse all sizes and packs.
All BAC Water Supply products are supplied for laboratory research use only and are not for human or veterinary use.