# Bacteriostatic Water Explained

Bacteriostatic water is sterile water with a small amount of preservative, usually 0.9% benzyl alcohol, which slows bacterial growth so a vial can be entered more than once. Its storage and how long it can be used after opening are set by its manufacturer and printed on the label.

Canonical: https://bestpeptidecalculator.app/guides/bacteriostatic-water-storage
Last reviewed: 2026-11-08

## What bacteriostatic water is

|  | Bacteriostatic water | Sterile water |
| --- | --- | --- |
| Sterile | Yes | Yes |
| Preservative | Yes (commonly 0.9% benzyl alcohol) | No |
| Vial entries | Multiple, within the label’s limit | Usually single use |
| Effect on the calculation | None | None |

For the calculator, the liquid type doesn’t matter: only its volume does.

## Storage and use-by: read the label

Storage temperature and how long an opened vial may be used are stated by each manufacturer, and they differ between products. The label and package insert are the source to follow, and the label of the specific product you have wins over any general rule.

- Look for the storage temperature range on the vial or carton.
- Look for a limit on use after the first puncture (a number of days).
- Write the date you first opened the vial on its label.

> We don’t estimate shelf life or storage times. When the label says nothing, contact the supplier.

## Reconstituted peptides are a different question

How long a peptide solution keeps depends on the peptide, not the water. That information comes from the peptide supplier’s data. See [how to reconstitute peptides](https://bestpeptidecalculator.app/guides/how-to-reconstitute-peptides) for the math side.

## Frequently asked questions

### What is bac water?

Bacteriostatic water: sterile water with a preservative (commonly 0.9% benzyl alcohol) so the vial can be entered more than once.

### Does bac water need to be refrigerated?

Follow the storage temperature on your product’s label; manufacturers state it and it varies between products.

### How long is bac water good for once opened?

The manufacturer’s label gives the limit for an opened vial. Use that figure for your product.

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Research and educational use only. Not medical advice. Best Peptide Calculator is powered by Peptide Library (https://peptidelibrary.app).