What Is Bacteriostatic Water?

What "bacteriostatic" means

Bacteriostatic means "stops bacteria from growing." It holds germs back, but it does not wipe them all out.

Think of it like a fridge, which slows down spoiling but does not make old food fresh. In the same way, the preservative slows down germs that get into the vial. That is why the 28 day limit below still matters.

The label calls benzyl alcohol a "bacteriostatic preservative." That is where the name comes from.

What is in it

The label lists just two parts:

• Water for injection. This is very pure, sterile water.
• Benzyl alcohol. This is the preservative.

The benzyl alcohol comes in one of two strengths, based on the vial:

• 0.9%, which is 9 mg in each mL, in plastic vials.
• 1.1%, which is 11 mg in each mL, in glass vials.

The label lists the pH as 5.7, with a range of 4.5 to 7.0. pH is a scale for how acidic a liquid is. 7 is neutral.

What bacteriostatic water is used for

The label says it is only for diluting or dissolving drugs. Diluting means thinning a liquid drug. Dissolving means turning a dry powder into a liquid, which is also called reconstituting.

The mixed drug may then be given into a vein, a muscle or under the skin. The label says to do this only the way the drug maker says.

It comes in a multiple-dose vial, so you can draw from it more than once, and the preservative is what makes that possible.

People also use it to reconstitute peptide powders. Bacteriostatic water for peptides covers that use, and how to reconstitute peptides walks through the steps.

What it is not for

The label lists clear limits. Do not use it:

• For newborns. Benzyl alcohol can be toxic to newborn babies. In 1982, CDC reported newborn deaths linked to it, and a medical journal described the same harm as a "gasping syndrome" (Gershanik and others, 1982). For newborn drugs, the label says to use only sterile water with no preservative.
• On its own into a vein. Given into a vein with nothing mixed in, it can burst red blood cells. This is called hemolysis. The label says it must be made close to the body's own salt balance before it goes into a vein.
• To replace lost body fluid. It is not a drip for fluids.
• For spinal or epidural procedures. The label rules this out.
• With a drug that does not mix with benzyl alcohol. Some drugs do not. The label says to ask a pharmacist.

Bacteriostatic water vs sterile water

The main difference is the preservative.

Which one to use depends on the drug. The bacteriostatic water label says to follow the drug maker's instructions. Read more in bacteriostatic water vs sterile water.

How long it lasts once opened

CDC guidance says to date a multi-dose vial when you first open it. It says to throw it out within 28 days, unless the maker says otherwise. USP chapter 797, a pharmacy standard, sets the same 28 days for opened vials that contain a preservative.

The 28 day rule is not printed on the bacteriostatic water label. It comes from CDC and USP. The label itself only gives an expiry date for the sealed vial.

The 28 days is a safety limit for germs, not a sign that the water turns into something else. For more, see how long bacteriostatic water lasts.

How to store it

The label says to store it at 20 to 25 C, which is 68 to 77 F. That is normal room temperature.

The label does not specify refrigeration. See does bacteriostatic water need to be refrigerated for the details.

The label also says not to use it unless the liquid is clear and the seal is intact.

Read the label

Here is what one bacteriostatic water label on DailyMed says, in plain words. The link is in the sources below.

The 28 day limit for an opened vial is not on this label. It comes from CDC and USP, as shown above.