What is Bacteriostatic Water?

Bacteriostatic water is sterile water with 0.9% benzyl alcohol added as a preservative. It is often called bac water. The benzyl alcohol is there to stop bacteria multiplying in a vial that is opened more than once.

What the word means

Bacteriostatic means it stops bacteria growing. It does not kill them. That is the difference between a preservative and a disinfectant.

What is in it

Ingredient	Amount
Sterile water	Makes up the rest of the vial
Benzyl alcohol	0.9% (9mg per ml)

How it differs from plain sterile water

Plain sterile water has no preservative in it. Once a vial is opened it is normally used once and thrown away. Bacteriostatic water has the preservative, so the vial is designed to be opened more than once. There is a full comparison on our page bacteriostatic water vs sterile water vs saline.

How it is supplied

It usually comes in small sealed glass vials with a rubber stopper and a crimped cap. We sell 10ml vials. The vials are kept at room temperature, away from direct sunlight.

Bacteriostatic water in the UK

In the UK there is a licensed bacteriostatic water, made by Pfizer and supplied as a diluent for one specific medicine. It is a prescription-only medicine. You can see its product information on the Electronic Medicines Compendium.

The bacteriostatic water we sell is a laboratory supply. It is not a licensed medicine and it is sold for laboratory use only, not for human or veterinary use. We explain the difference on this page.

Where to buy it

You can buy 10ml vials of bacteriostatic water from us in boxes of 3 to 1,000, from UK stock. See buy bacteriostatic water in the UK.