What Is Bacteriostatic Water?

Bacteriostatic water is sterile water containing 0.9% sodium chloride and, critically, 0.9% benzyl alcohol as a preservative. It is not a research compound in its own right — it is a consumable, used to reconstitute lyophilised peptides from powder into solution.

The benzyl alcohol is what distinguishes it from ordinary sterile water for injection. It inhibits bacterial growth, which is why a vial can be entered more than once over a period of days rather than being discarded after a single use. Sterile water without a preservative offers no such protection and is a single-use product.

How It Is Used in Reconstitution

The diluent is introduced slowly down the inside wall of the peptide vial rather than directed at the lyophilised cake. Peptides are surfactant-sensitive and a jet of liquid striking the powder directly can shear the molecule. The vial is then swirled, never shaken, until the solution clears.

The volume chosen determines concentration, and that is arithmetic rather than convention: 2ml added to a 10mg vial gives 5mg/ml. Our reconstitution calculator handles the working if you would rather not do it by hand.

Storage and Shelf Life

Unopened, bacteriostatic water is stable at room temperature until its printed expiry. Once the stopper has been pierced, the preservative is generally considered effective for around 28 days, and the vial should be refrigerated in the interim.

The stopper should be wiped with an alcohol swab before every entry. The preservative inhibits growth; it does not sterilise a contaminated surface, and assuming otherwise is the most common handling error with multi-dose vials.

Regulatory Status

Bacteriostatic water supplied for laboratory use is a research consumable. It is not supplied as a medicine and is not intended for human or veterinary administration. Benzyl alcohol is not suitable for all applications, and any research protocol should account for its presence rather than treating the diluent as inert.

Frequently Asked Questions

What is the difference between bacteriostatic and sterile water?

Bacteriostatic water contains 0.9% benzyl alcohol as a preservative, which inhibits bacterial growth and allows a vial to be entered multiple times. Sterile water has no preservative and is single-use.

How long does bacteriostatic water last once opened?

The preservative is generally considered effective for about 28 days after first entry. Refrigerate between uses and swab the stopper each time.

How much should be added to a peptide vial?

That depends on the concentration required. 2ml into a 10mg vial gives 5mg/ml. The volume is a calculation, not a fixed rule.

Is bacteriostatic water a peptide?

No. It is a diluent — a consumable used to reconstitute lyophilised peptides. It has no research activity of its own.

Products discussed in this guide are for research and laboratory use only. AllMyPeptides does not condone or support misuse of any research materials. Not for human or animal consumption.

What Is Bacteriostatic Water? Reconstitution Guide