What is bacteriostatic (bac) water?

Bacteriostatic water is sterile, purified water to which 0.9% benzyl alcohol has been added as a preservative. The benzyl alcohol disrupts bacterial cell membranes and stops any organism introduced during a needle entry from multiplying inside the vial. That is what makes it a multi-draw diluent: one opened vial can be drawn from repeatedly for up to 28 days, which is why it is the diluent specified on every lyophilised peptide page at Omega Peptides Australia.

It goes by many names in search. Bac water and BAC water are the common short forms, and it is often typed as bacwater, back water, bac wayer, bacstat water, bacteria static water or bacterial water. Labels call it bacteriostatic water for injection, and researchers often search bacteriostatic water for peptides. All of these refer to the same product: water plus 0.9% benzyl alcohol, nothing else.

What you need before you reconstitute

How to reconstitute peptides: step by step

The method below is the same for every lyophilised peptide, from a 5mg BPC-157 vial to a 60mg retatrutide vial. Only the volume of water changes, and that is set by the concentration you want (see the table in the next section).

1. Bring both vials to room temperature Take the peptide vial out of the fridge or freezer and leave it for 15 to 20 minutes. Adding water to a cold vial can cause condensation and makes the powder harder to dissolve.
2. Clean your work surface and hands Work on a clean bench, wash hands, and lay out the peptide vial, bacteriostatic water, a sterile syringe and alcohol swabs.
3. Swab both rubber stoppers Remove the flip caps and wipe the stopper on the peptide vial and on the bacteriostatic water vial with an alcohol swab. Let them air dry for a few seconds.
4. Decide the water volume Divide the vial size in mg by the concentration you want in mg/mL. For a 10mg vial at 5 mg/mL, that is 2mL of water. Use the reconstitution calculator if you prefer not to do it by hand.
5. Draw the bacteriostatic water Pull air into the syringe equal to the water volume, insert through the stopper of the bac water vial, push the air in (this keeps pressure even), invert the vial and draw the measured volume of water. Tap out any air bubbles.
6. Add the water slowly down the glass Insert the needle through the peptide vial stopper at an angle and aim the tip at the inside wall of the vial, not directly onto the powder. Release the water slowly so it runs down the glass. Spraying water straight onto the powder can damage peptide chains and cause foaming.
7. Swirl, do not shake Roll the vial gently between your fingers or swirl it in a small circle until the powder has fully dissolved and the solution is clear. Shaking creates foam and shears the peptide. Most peptides dissolve within a minute or two; a few, such as larger or more hydrophobic sequences, may take several minutes of gentle swirling.
8. Label and refrigerate Write the peptide name, concentration (mg/mL), and reconstitution date on the vial. Store upright at 2 to 8 degrees Celsius, protected from light, and use within 28 days.

Peptide reconstitution concentration table

The formula is simple: concentration (mg/mL) = peptide in the vial (mg) ÷ bacteriostatic water added (mL). On a standard U-100 insulin syringe, 100 units equals 1mL, so 1 unit is 0.01mL and 10 units is 0.1mL. The table shows the concentration and the amount of peptide contained per unit and per 10 units for the vial sizes Omega stocks.

For any other combination, the Omega peptide reconstitution calculator gives the concentration and per-unit values instantly. As a rule of thumb, more water gives a more dilute solution that is easier to measure accurately in small volumes, while less water gives a concentrated solution that takes up less fridge space and fewer draws per vial.

How to mix retatrutide with bac water (worked example)

Retatrutide is the peptide Australian researchers ask about most, and retatrutide reconstitution follows the exact method above. Retatrutide is supplied in 5mg, 10mg, 20mg, 30mg and 60mg vials, so the only decision is how much bacteriostatic water to add.

• 10mg retatrutide vial + 2mL bac water = 5 mg/mL. Each 10 units (0.1mL) contains 500mcg.
• 20mg retatrutide vial + 2mL bac water = 10 mg/mL. Each 10 units (0.1mL) contains 1,000mcg (1mg).
• 30mg retatrutide vial + 3mL bac water = 10 mg/mL. Each 10 units (0.1mL) contains 1,000mcg (1mg).
• 60mg retatrutide vial + 3mL bac water = 20 mg/mL. Each 10 units (0.1mL) contains 2,000mcg (2mg).

Retatrutide dissolves readily in bacteriostatic water. Add the water slowly down the inside of the vial, swirl gently until the solution is completely clear, then label and refrigerate. A 3mL bac water vial covers one retatrutide vial; the 10mL vial is the better value if you are reconstituting several vials or running a tirzepatide comparison alongside.

The same arithmetic applies to every other compound. A 5mg BPC-157 vial with 1mL of water is 5 mg/mL; a 50mg GHK-Cu vial with 5mL of water is 10 mg/mL; a 10mg TB-500 vial with 2mL is 5 mg/mL.

Storing peptides after reconstitution

For full storage guidance on lyophilised and reconstituted peptides, read the Omega peptide storage guide.

Common reconstitution mistakes

• Shaking the vial. The most common error. Shaking foams the solution and can denature the peptide. Swirl gently instead.
• Squirting water directly onto the powder. Run the water down the inside wall of the vial so it reaches the powder gently.
• Using sterile water or saline for a multi-draw vial. Without benzyl alcohol, an opened vial has no protection against contamination. Use bacteriostatic water for any vial drawn from more than once.
• Using distilled, boiled or tap water. None of these are sterile or preserved.
• Not recording the concentration. Without the mg/mL on the label, the per-unit peptide content is unknown. Label every vial at the time of reconstitution.
• Reconstituting a cold vial. Let the vial reach room temperature first to avoid condensation and slow dissolution.
• Keeping a reconstituted vial past 28 days. Peptide stability in solution and the preservative life of the bac water both run out at about the same point.
• Reusing a needle between vials. Use a fresh sterile syringe for the water draw, and never return solution to the bac water vial.

Bacteriostatic water in Australia: where to buy

Bacteriostatic water is not a standard over-the-counter line at Australian pharmacy chains such as Chemist Warehouse or Priceline, which is why "bac water australia" and "where can I buy bacteriostatic water" are such common searches. Overseas brands such as Hospira (Pfizer) 30mL bacteriostatic water are US pharmacy products and are not routinely stocked in Australia, so importing them means long shipping times and customs uncertainty.

Omega Peptides Australia holds bacteriostatic water in Australian stock in two sizes: the 10mL vial ($29.99), which is the better value for labs reconstituting several peptides, and the 3mL vial ($14.99) for a single vial or two. Both are 0.9% benzyl alcohol in sterile water, supplied with an independent certificate of analysis, and dispatched the same business day on orders placed before 12pm AEST. Syringes and swabs are stocked alongside, or bundled in the Starter Kit.

Frequently Asked Questions

What is bac water?

Bac water is short for bacteriostatic water: sterile, purified water with 0.9% benzyl alcohol added as a preservative. The benzyl alcohol stops bacteria multiplying inside an opened vial, which is why it is the standard multi-draw diluent for reconstituting lyophilised research peptides.

How do you reconstitute peptides?

Let the peptide vial reach room temperature, swab both vial tops, draw the chosen volume of bacteriostatic water into a sterile syringe, and add it slowly down the inside wall of the peptide vial. Swirl gently until the solution is clear (never shake), then label the vial with the concentration and date and refrigerate at 2 to 8 degrees Celsius.

How much bacteriostatic water do I add to a peptide vial?

It depends on the working concentration you want. Concentration in mg/mL equals the vial size in mg divided by the water volume in mL. Adding 2mL to a 10mg vial gives 5 mg/mL; adding 1mL to a 5mg vial gives 5 mg/mL. The Omega reconstitution calculator does the arithmetic for any vial size and water volume.

How do you mix retatrutide with bac water?

Retatrutide is reconstituted the same way as any lyophilised peptide. For a 10mg retatrutide vial, adding 2mL of bacteriostatic water gives 5 mg/mL, so each 0.1mL (10 units on a U-100 syringe) contains 500mcg. Add the water slowly down the glass, swirl gently until clear, and store the reconstituted vial refrigerated.

Can I use sterile water instead of bacteriostatic water for peptides?

Sterile water for injection contains no preservative, so it is only suitable for a vial that will be used once. For any vial drawn from more than once over days or weeks, bacteriostatic water is the correct diluent because the 0.9% benzyl alcohol keeps the solution usable for up to 28 days.

How long does a reconstituted peptide last?

Once reconstituted with bacteriostatic water and stored at 2 to 8 degrees Celsius, most research peptides remain stable for around 28 days, which matches the usable life of an opened bacteriostatic water vial. Some peptides are less stable in solution, so check the product page for compound-specific storage notes.

Where can I buy bacteriostatic water in Australia?

Omega Peptides Australia stocks bacteriostatic water in 10mL and 3mL vials in Australia, dispatched same day on orders placed before 12pm AEST, with a certificate of analysis for every batch. It is not usually stocked over the counter at Australian pharmacies such as Chemist Warehouse or Priceline.

Is bacteriostatic water the same as bacteriostatic saline?

No. Bacteriostatic saline contains 0.9% sodium chloride as well as 0.9% benzyl alcohol. Bacteriostatic water contains only water and benzyl alcohol, and is the diluent specified for peptide reconstitution.

What does bacteriostatic water for peptides mean?

It is the same product as bacteriostatic water for injection: sterile water with 0.9% benzyl alcohol, supplied in a multi-draw vial. The phrase simply describes its main laboratory use, reconstituting lyophilised peptide powders into a working solution.