Bacteriostatic water for research: the laboratory guide (USP, 0.9 % benzyl alcohol, COA, storage)

The name comes from a monograph of the United States Pharmacopeia (USP).

The monograph defines a sterile, non-pyrogenic water to which one or more antimicrobial preservatives have been added, filled into multiple-withdrawal containers, with a pH between 4.5 and 7.0 and no added salt, buffer or sugar.

On the American market the preservative is almost always benzyl alcohol at 0.9 % (9 mg per mL), and the label says so.

Two words in the name do two different jobs. Sterile describes how the water was made: filtered, filled and sealed so that nothing lives in it at the time of filling.

Bacteriostatic describes what the preservative does afterward: it keeps bacteria from multiplying once the septum has been pierced and the vial is open to the air.

The preservative does not sterilize a contaminated liquid; it holds an already sterile one.

In a research setting this water is the standard solvent for the lyophilized peptides of this catalog, such as GHK‑Cu, BPC‑157 and TB‑500.

It is described and sold here as a laboratory supply only. Research use only. Not for human or veterinary use.

Benzyl alcohol (C₇H₈O, 108.1 g/mol) is an aromatic alcohol, a clear liquid with a faint almond-like odor, miscible with water at the concentration in question.

At 0.9 % it is bacteriostatic and, for most organisms, also fungistatic: it stops growth. That is the whole of its role.

The 28-day figure is the reason the water exists. Plain sterile water has no preservative; once its vial is opened, the USP expects it to be discarded.

A bacteriostatic vial is designed to be pierced several times over four weeks, which is why the septum is a self-sealing bromobutyl rubber and why the label carries a "discard after opening" instruction.

Plain sterile water and bacteriostatic water are compared point by point in the bacteriostatic water buying guide.

Three sizes cover the market, and each has its own history.

• 30 mL is the hospital-supply size, made in the United States by Hospira (a Pfizer company) and by a small number of other pharmaceutical manufacturers. "Hospira bacteriostatic water" is searched forty thousand times a month because that one product has been intermittently out of stock across the whole market for years, and because its 30 mL flint-glass vial is what most people picture when they hear the name.
• 10 mL is the traditional laboratory size: a glass vial with a rubber stopper and crimp cap, sold by laboratory-supply houses and by research-peptide suppliers.
• 3 mL is the size that fits a research order: one small vial per lot, enough for the lyophilized vials it ships with, nothing left over past 28 days. It is the size listed in the OXpeptides catalog.

Whatever the size, a vial is a laboratory supply only if the label carries four things: the words "Bacteriostatic Water" and "USP", the preservative and its concentration ("0.9 % benzyl alcohol"), a printed lot number, and an expiry date.

A bottle without a lot number is a bottle of water.

The glass matters too. Type I borosilicate is the standard for a multiple-withdrawal vial; it does not leach alkali into a liquid stored for two years.

The septum is bromobutyl rubber (self-sealing after a puncture, low permeability to gas) and the closure an aluminum crimp with a plastic flip-off disc that shows whether the vial has been opened.

A certificate of analysis for bacteriostatic water is shorter than one for a peptide, and every line on it is a pass/fail test against the monograph rather than a purity percentage. A complete one shows:

Three details separate a certificate from a document. First, the lot number on the page must be the lot number on the vial.

Second, the benzyl alcohol line must be an assay, a measured value, and not a copy of the label.

Third, the certificate comes from the manufacturer (water is not sent to Janoshik the way a peptide is), so the manufacturer's name on the certificate must match the manufacturer on the label.

A supplier that re-bottles water and shows another company's certificate has broken the chain.

The same reading discipline applies to peptide certificates, field by field, in how to read a peptide COA. OXpeptides publishes its lot documents in the COA library.

Everything else in a research order goes cold. Bacteriostatic water does not.

• Temperature: 20 to 25 °C, the controlled room temperature of the monograph, with excursions between 15 and 30 °C allowed. Never freeze it. Ice expands and can crack the vial, and benzyl alcohol separates from ice, so a thawed vial no longer has a uniform 0.9 %.
• Light: in the box. Benzyl alcohol oxidizes slowly under light to benzaldehyde, which is the source of a stronger almond odor in an old, light-exposed vial.
• Sealed shelf life: 24 months for most makers, printed on the label. The date governs, not the appearance.
• After the first puncture: 28 days, the period the preservative is qualified for. Write the date of first use on the label.

Between the freezer for the peptides and the shelf for the water, a research bench holds two storage lines. The cold line, compound by compound, is in lyophilized peptides: storage and shelf life.

Water is inexpensive, and a suspect vial is never worth keeping. Discard it when:

1. The liquid is not clear. Cloudiness, a haze that moves when the vial is tilted, floating particles or a yellow tint all mean the lot has failed the appearance test in front of you.
2. The seal is not intact. A missing flip-off disc, a lifted crimp or a septum with a visible hole on arrival means the vial was opened before you.
3. The label is incomplete. No lot number, no expiry date, no concentration of benzyl alcohol, or a hand-written label.
4. The vial was frozen. A cracked vial, or a vial that arrived frozen in winter shipping, is discarded even if it looks clear once thawed.
5. 28 days have passed since the first puncture, or the printed expiry date has passed.

OXpeptides lists a 3 mL vial of bacteriostatic water, USP, 0.9 % benzyl alcohol, next to every lyophilized compound, so the solvent and the powders it accompanies ship in one parcel, from one source, under one lot discipline.

The vial carries a printed lot number and expiry date; the document of each lot joins the COA library as the lot is received. It ships from California to the United States and from France to Europe.

For sizes, prices and the plain-water comparison, see the bacteriostatic water buying guide. For the vial itself, see bacteriostatic water in the catalog →