Bac water: what is bacteriostatic water?

Bacteriostatic water is sterile water with 0.9% benzyl alcohol added. Benzyl alcohol is a preservative: it inhibits the growth of bacteria in the liquid. That is where the name comes from — bacteriostatic means bacterial growth is inhibited, not that bacteria are killed.

The water itself has no biological activity. Bac water is a laboratory supply, not an active substance: it only serves to dissolve a powder or to dilute a solution.

Both are filled sterile, but they are meant for different use. The difference is the preservative.

• Sterile water contains no preservative. Once the vial's septum has been pierced, sterility is no longer guaranteed, so it is meant for single use.
• Bac water contains 0.9% benzyl alcohol. A vial can therefore be pierced several times within its shelf life, which helps when you work with the same stock solution over several days.
• Benzyl alcohol does not suit every material: some proteins and cell cultures do not tolerate it. Always follow your lab's protocol or the material's data sheet.

Work out the concentration of your solution (mg/ml or µg/ml) with the peptide calculator. How to dissolve a vial step by step is in Dissolving peptides.

• Reconstitution: dissolving freeze-dried research material, such as BPC-157 or TB-500, into a solution of known concentration.
• Dilutions: making a dilution series from a stock solution.
• Working over several days: thanks to the preservative you can reuse one vial within its shelf life.

Most peptides dissolve well in bac water. Some peptides rich in basic amino acids dissolve poorly at neutral pH; for those, labs often use acetic acid water, sterile water with dilute acetic acid. The material's data sheet or certificate tells you which solvent fits.

• Unopened: keep the vial at room temperature, out of direct sunlight, until the expiry date on the label.
• Opened: common lab guidance is to use up a pierced vial of bac water within about 28 days.
• With a dissolved peptide in it: keep the solution in the fridge (2–8 °C) and do not freeze it.
• Discard a solution that turns cloudy, changes colour or contains particles.

BrabantLabs supplies bac water in 3 ml and 10 ml vials, shipped from the Netherlands and delivered within 1–2 working days.

• A sealed vial with cap and septum, so you can work sterile.
• A clear composition on the label: sterile water with 0.9% benzyl alcohol.
• A lot number and an expiry date.
• A volume that suits your work: 3 ml for a single vial, 10 ml when you dissolve several vials.

Many people look for bac water at the pharmacy. Whether a pharmacy can order bacteriostatic water for you differs per pharmacy. For laboratory use you buy it from a supplier of lab supplies, with a label, lot number and expiry date.

Is bac water the same as distilled water?

No. Distilled water is purified, but it is not packed sterile and contains no preservative, so it is not suitable as a sterile solvent for research material.

How long does bac water keep?

Unopened, until the date on the label. A pierced vial is used up within about 28 days, following common lab guidance.

Does bac water need to go in the fridge?

An unopened vial does not: keep it at room temperature, out of direct light. Once a peptide is dissolved in it, the solution goes in the fridge (2–8 °C).

Can I use sterile water instead of bac water?

Yes, if you use the solution in one go. Sterile water has no preservative, so for a vial you pierce over several days bac water is the usual choice.

• View Bac water in the shop