What is ? Bacteriostatic water, explained

01

What bacteriostatic water is

The official US label for Bacteriostatic Water for Injection describes a sterile, nonpyrogenic water containing 0.9% (9 mg/mL) or 1.1% (11 mg/mL) benzyl alcohol, added as a bacteriostatic preservative. Its pH is 5.7, within a range of 4.5 to 7.0.

“Bacteriostatic” means it slows bacterial growth; it does not sterilize a contaminated vial. Benzyl alcohol itself is a simple aromatic alcohol, C7H8O (PubChem CID 244).

Sources: [1] DailyMed · Bacteriostatic Water for Injection, USP · [4] PubChem · benzyl alcohol

02

Why the preservative matters

The label describes a multiple-dose container from which repeated withdrawals may be made. Plain sterile water has no preservative and comes only in single-dose containers, with the unused portion discarded.

CDC material for healthcare workers draws the same line: multiple-dose vials typically contain a preservative to help limit bacterial growth, and single-dose vials typically do not. Preservatives have no effect on viruses, so technique still matters.

Sources: [1] DailyMed · Bacteriostatic Water for Injection, USP · [2] DailyMed · Sterile Water for Injection, USP · [3] CDC · Single-dose or multi-dose?

03

What it is used for in the lab

Lyophilized peptides arrive as dry powder. Adding a measured volume of bacteriostatic water dissolves the powder at a known concentration, a step called reconstitution.

Concentration is the vial’s content divided by the volume added: 10 mg of peptide in 2 mL of water gives 5 mg per mL. The reconstitution calculator handles other combinations.

The label also notes that some compounds are incompatible with benzyl alcohol, so follow the preparation described for the material you are working with.

Sources: [1] DailyMed · Bacteriostatic Water for Injection, USP

04

Bacteriostatic vs sterile water

The short version: a preserved, multiple-use vial versus an unpreserved, single-use one. The full comparison: bacteriostatic vs sterile water.

05

How long it lasts

Unopened, keep it at room temperature. Once opened, keep it in the fridge at 2 to 8 °C and use it within about 6 weeks, the same timeline as a mixed peptide vial; it can last up to 12 weeks. For how healthcare settings handle bacteriostatic water in general, see how long bacteriostatic water lasts.

06

How is documented

Every batch is independently tested for purity and content, with its certificate of analysis ready to verify. Match the lot number on the vial to the report before use, and store the vial as its label directs.