What Is Bacteriostatic Water? Bac Water Explained
Bacteriostatic water is the standard liquid for reconstituting research peptides. Here is what is in it, how the preservative works, how it compares with sterile water and saline, and how to store it.
What is bac water?
Bac water is short for bacteriostatic water: sterile water that contains a small amount of preservative so it can be drawn from more than once. It is the most common liquid for reconstituting lyophilised peptides, which is why researchers often search for "bac water for peptides" or "bacteriostatic water for peptides".
- Base
- Sterile water
- Preservative
- 0.9% benzyl alcohol
- Use
- Multi-dose vials
- After opening
- Commonly 28 days
What is in bac water?
Just two things: sterile water and 0.9% benzyl alcohol. That works out to about 9mg of benzyl alcohol in every millilitre.
- Sterile water~99%
- Benzyl alcohol9mg (0.9% w/v)
"Bacteriostatic" means it holds back bacterial growth rather than killing every bacterium (that would be bactericidal). The benzyl alcohol keeps any bacteria introduced by a needle from multiplying, which is what makes a multi-use vial practical.
Bac water vs sterile water vs saline
| Liquid | Contains | Multi-use? | Typical lab use |
|---|---|---|---|
| Bacteriostatic water | Water + 0.9% benzyl alcohol | Yes | Reconstituting most peptides |
| Sterile water | Water only | No, single use once opened | One-off reconstitution |
| Bacteriostatic saline | 0.9% sodium chloride + benzyl alcohol | Yes | Compounds that prefer a salt solution |
For most peptides bac water is the default. A few compounds dissolve better in a slightly acidic or saline solution, so check the supplier's handling notes for anything unusual.
Why bac water is used for peptides
- Multi-use: a reconstituted peptide vial is usually drawn from many times.
- Neutral: it does not change the peptide's structure for most compounds.
- Simple maths: because it is just water, the concentration is easy to calculate.
Storing bac water
Unopened vials keep at room temperature until their expiry date. Once punctured, store the vial in the fridge, wipe the stopper before each use, and follow the discard period on the label. Commonly that is 28 days, the standard guideline for multi-dose vials unless the manufacturer says otherwise.
Buying bac water in Australia
We sell bacteriostatic water in 3ml and 10ml vials, and it is included in our peptide starter kit with insulin syringes and alcohol wipes.
Further reading
For laboratory research use only. Not for human consumption. Not medical or legal advice.
