Bacteriostatic water: what it is, how it is kept and what its certificate carries

Written 24 September 2026, last changed 2 November 2026 by the trade desk. About 4 minutes to read.

Bacteriostatic water is water with 0.9 percent benzyl alcohol, a preservative that holds back microbial growth. Sealed vials are kept at room temperature, 15 to 25 degrees Celsius, and never frozen; it is sold here as BAC3 and BAC10.

What it is

Bacteriostatic water is water with 0.9 percent weight in volume of benzyl alcohol dissolved in it, filtered and filled into a glass vial. Benzyl alcohol is a small aromatic alcohol, soluble in water to about 4 percent, so at 0.9 percent it is fully dissolved, and its job in the vial is to hold back the growth of microorganisms. The water is otherwise plain: no salt, no buffer, no other additive. We list it as BAC3 (3 mL) and BAC10 (10 mL), ten vials to a box. Sold 10 boxes at a time: bacteriostatic water ships in its own parcel.

Unopened storage

Sealed vials are kept at room temperature in their carton. The storage line on the product page reads 15 to 25 degrees Celsius, the European convention for room temperature. They do not need a refrigerator, and they must never be frozen: ice expanding inside a filled glass vial can crack it, and the label says do not freeze. Each vial carries its batch number; the retest date is on the batch record, and the certificate for the batch is found on the certificate page like any other line.

The specification it is released against

The certificate for a batch of bacteriostatic water differs from a peptide certificate: there is no purity line, and identity is conformance to the article specification rather than a measured mass. The lines are the six on the product page's release table, and the identity line is where the tests on the water itself sit. Its certificate reports appearance, identity (conformance to the article specification) and the fill. The article specification behind the identity line covers the benzyl alcohol content against the 0.9 percent w/v label claim, the pH and a water-quality check; the desk answers for them on a particular batch, and for whether that batch was tested for sterility or endotoxin.

The certificate carries the batch number and the date of analysis at the top, and the batch number on the box, printed or behind its QR code, is what is looked up.

When preservative-free sterile water is used instead

Benzyl alcohol is not inert to every method: it absorbs in the ultraviolet, including at 220 nm, where peptide purity is taken, and it has a mass of 108. Some written methods simply specify preservative-free water, and then sterile water without preservative is used. Preservative-free sterile water is not on our list at present, so it is sourced separately.

Handling in short

• Room temperature unopened, never frozen.
• Upright, in its carton.
• One batch number per vial, checked on the certificate page.
• Preservative-free water when the method says so.

Applies to

This guide is about Bacteriostatic Water and no other line; the full list is on the compounds page.

Questions about bacteriostatic water

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