What Is Bacteriostatic Water? A Laboratory Reconstitution Primer

Before a lyophilized peptide can be used in most experiments, it has to be dissolved in a suitable diluent. The most common choice in peptide research is bacteriostatic water. This primer explains what it is, how it differs from plain sterile water, and the basics of reconstitution technique.

What bacteriostatic water is

Bacteriostatic water is sterile water containing 0.9% benzyl alcohol. The benzyl alcohol is a preservative that inhibits bacterial growth. It does not sterilize, but it keeps bacteria from multiplying. This allows a vial to be punctured multiple times over its use period.

Bacteriostatic water vs. sterile water

	Bacteriostatic water	Sterile water
Preservative	0.9% benzyl alcohol	None
Use	Multi-use vials	Single use
Typical role	General peptide reconstitution	Applications where a preservative is undesirable

Some peptides, or some experimental systems, are incompatible with benzyl alcohol. In those cases, researchers may use sterile water, dilute acetic acid, or another solvent recommended for that specific compound.

Basic reconstitution technique

1. Let both the peptide vial and the diluent reach room temperature.
2. Wipe both vial stoppers with an alcohol swab.
3. Draw the planned volume of diluent with a sterile syringe.
4. Insert the needle into the peptide vial and let the diluent run slowly down the inside wall of the vial. Do not spray it directly onto the powder.
5. Gently swirl or roll the vial until the powder dissolves. Avoid vigorous shaking, which can cause foaming and aggregation.
6. Label the vial with the reconstitution date and concentration, then refrigerate at 2–8 °C.

Calculating concentration

Concentration is simply the peptide mass divided by the diluent volume. For example, 10 mg of peptide dissolved in 2 mL of diluent gives a concentration of 5 mg/mL. Recording this on the vial prevents errors later.

Azyrion Labs supplies Bacteriostatic Water alongside our research compounds in the Lab Supplies collection. For storage guidance after reconstitution, see Lyophilized Peptide Storage and Handling.