Bacteriostatic Water vs Sterile Water

The short answer

• Bacteriostatic water is sterile water plus benzyl alcohol. It comes in a vial made for more than one use.
• Sterile water for injection is sterile water with nothing added. It comes in a vial made for one use.
• Both labels say to store the vial at 20 to 25 C (68 to 77 F).
• The label of the drug you are mixing decides which one to use, not the water label.

What is bacteriostatic water?

Bacteriostatic water is sterile water for injection with benzyl alcohol added. The label lists 0.9% (9 mg per mL) in plastic vials and 1.1% (11 mg per mL) in glass vials. The benzyl alcohol is there as a preservative.

"Bacteriostatic" means it holds back the growth of bacteria, not that it kills every germ. The label calls the vial a multiple-dose container, which means you can draw from it more than once. For more on what it is, see what is bacteriostatic water.

What is sterile water for injection?

Sterile water for injection is just water made for use with drugs. It has no preservative. The label says it has no bacteriostat, no antimicrobial agent and no added buffer.

It comes only in single-dose vials. The label says not to reuse the vial, so any water left over is thrown out.

Side-by-side label comparison

This table is built from the two drug labels on DailyMed. Each row is what the label itself says.

Hemolysis means red blood cells break open. Both labels warn about it for water put into a vein with nothing mixed in.

Why the preservative matters

A needle that goes into a vial can carry germs in with it. The preservative in bacteriostatic water slows their growth. That is why one vial can be entered more than once.

It still has a time limit once opened. The CDC says to date an opened multiple-dose vial and throw it out within 28 days, unless the maker gives a different date. USP chapter 797 sets the same 28 days.

The 28 days is not on the bacteriostatic water label. The label gives a storage range and nothing else about time. The 28 days comes from the CDC and USP. Read more in how long bacteriostatic water lasts.

Sterile water has no preservative, so there is no 28-day window: you use the vial once and throw out the rest.

When each one is used

Both labels say the same thing about use: they are only for diluting or dissolving drugs, and they say to follow the drug maker's own directions for which liquid to use.

So the answer is on the label of the product you are mixing, not on the water. The labels also warn that some drugs may not mix well in a liquid that has benzyl alcohol.

Which one does my product ask for?

1. Read the label or insert of the product you are mixing. Does it name a liquid?
2. Does it warn against benzyl alcohol or preservatives?
3. Is it for a newborn? If so, the label says preservative-free sterile water only.
4. Will you draw from the vial more than once? Only a multiple-dose vial is made for that.
5. Still not sure? Ask a pharmacist. Both labels say to consult one.

Once you know the liquid, our calculator does the mixing math. For how bacteriostatic water is used with peptide powders, see bacteriostatic water for peptides.

Who should not use bacteriostatic water

The label is clear that bacteriostatic water is not for use in newborns, because benzyl alcohol has been linked to harm in babies this young.

The label says to use only preservative-free sterile water when mixing drugs for a newborn. In 1982 the CDC reported deaths of newborns linked to benzyl alcohol. The babies had gasping breathing. A New England Journal of Medicine paper the same year named it the gasping syndrome and tied it to benzyl alcohol (Gershanik and others, 1982). Those reports are one reason for the warning.

What about distilled water or saline?

Neither label mentions distilled water. Both labels are for water made and tested for use with drugs. Ask a pharmacist before you swap in any other water.

Saline is salt water. Neither label lists salt. So bacteriostatic water is not saline, and sterile water is not saline either. Bacteriostatic saline is a different product with its own label.