# Bacteriostatic water, without the guesswork

This is an independent guide. It is not a pharmacy or a shop, and nothing is sold here. It explains the bottle, the label, and the questions that belong with a pharmacist.

## What is in the bottle?

Bacteriostatic water is sterile water with a small amount of benzyl alcohol. The benzyl alcohol is a preservative. It helps hold back the growth of bacteria after the bottle has been entered.

That does not make the water self-cleaning. The preservative does not protect against viruses. It also does not give complete protection from bacteria.

The bottle has one narrow job. It is used with medicines that need a liquid before injection. The medicine's own instructions decide whether this is the right liquid.

The label warns that plain bacteriostatic water placed into a vein can make red blood cells burst. It is a diluent, not a fluid replacement.

## Four similar names, four different jobs

- **Bacteriostatic water:** sterile water and benzyl alcohol, in a multiple-dose bottle, for use as a prescription diluent.
- **Sterile water:** sterile water without a preservative, in a single-dose bottle. Unused liquid is discarded.
- **Plain saline:** sterile salt water. It can replace fluid and salt.
- **Bacteriostatic saline:** sterile salt water and benzyl alcohol, in a multiple-dose bottle, for use as a diluent.

## The other medicine sets the rules

The approved water label does not give one mixing amount. It says the amount depends on the medicine, its strength, and how it will be given. It points back to that medicine's instructions.

The medicine's current label sets the liquid and amount. A pharmacist or prescriber checks that answer. This guide does not publish volumes, formulas, syringe units, or mixing steps.

## Opened bottles have a second clock

There is a printed expiration date for the sealed bottle. A shorter clock begins when a needle first enters a multi-dose vial.

CDC guidance says an opened multi-dose vial should be dated and discarded within 28 days unless the maker gives another date. The bacteriostatic water label itself does not print a 28-day rule.

The unopened bottle's label says to store it at 68°F to 77°F, which is 20°C to 25°C. The label does not direct storage in a refrigerator or freezer.

## Why the newborn warning is so firm

The approved label carries a boxed warning: bacteriostatic water must not be used in newborn babies. The concern is the benzyl alcohol preservative.

CDC reported in 1982 that benzyl-alcohol-preserved saline was linked to the deaths of 16 premature babies in two hospitals. The fluid in those reports was bacteriostatic saline, not bacteriostatic water. The shared concern was the preservative.

## The online market

“Bac water” is a short name people use for bacteriostatic water. Online listings may say “research use only” or “not for human consumption.” FDA has repeatedly looked past those notices to how a product is presented and intended to be used.

An NDC number is not proof of approval. Check the NDC Directory, the application in Drugs@FDA, and the full label on DailyMed. The approved US product points to NDA 018802 and carries the newborn warning.

## Price and shortage

Observed cash and list prices on September 17, 2026 ran from about $14 to $27 for one approved 30 mL vial. Unapproved online listings observed that day were about $8 to $13 per vial. These are market observations, not offers.

The FDA shortage record was current on September 17, 2026. It was first posted on December 3, 2021. A national pharmacy shortage bulletin cited manufacturing delays at the sole supplier.

## Continue

- [Common questions](https://purebacteriostaticwater.com/field-questions/)
- [Cost and supply notes](https://purebacteriostaticwater.com/cost-notes/)
- [Source trail](https://purebacteriostaticwater.com/source-trail/)