What is bacteriostatic water?

What is in it

The preservative is benzyl alcohol at 0.9 percent. The word bacteriostatic means that it holds bacterial growth in check. It does not turn an unsterile liquid into a sterile one: the water is sterile when it is made and sealed, and the preservative is there to protect the vial after it has been opened.

How it differs from sterile water

• Sterile water has no preservative. Once the vial is opened it is meant to be used once, and the rest discarded.
• Bacteriostatic water is meant for a vial that is opened and sampled more than once, because the preservative restrains growth between uses.
• Some experiments cannot tolerate benzyl alcohol. If yours cannot, use sterile water and plan to use each vial in one go.

Handling an opened vial

Wipe the stopper with an alcohol swab before every use, use a fresh sterile syringe each time, and write the date you first opened the vial on its label. Many protocols discard a multi-use vial after about four weeks. Follow the rule in your own protocol.

Reading the label

The label states the preservative and its percentage, a lot number and an expiry date. Do not use a vial past its expiry date, and note the lot number in your records so that a result can always be traced back to the materials behind it.

Where it fits

The pairing is simple. The freeze-dried peptide supplies the compound and the diluent supplies the liquid. Our post on reconstitution walks through the steps, and our post on storage covers what to do once the peptide is in solution.

A quick checklist

• Check the label for the preservative, the lot number and the expiry date.
• Wipe the stopper with an alcohol swab before every use.
• Write the date you first opened the vial on the label.

Research use only

Pep Pantry products are sold for laboratory research by adults. They are not for human or veterinary use. This article describes laboratory handling only.