Reconstitution Guide

How to Reconstitute Peptides with BAC Water

Published 2026-06-01 · Peptide Central Research Team · 8 min read

Every research peptide arrives as a lyophilised (freeze-dried) white powder. Before it can be used in any protocol, it must be reconstituted — dissolved into a sterile liquid. The standard solvent for this is bacteriostatic water (BAC water).

This guide covers everything: what BAC water is, how much to use, step-by-step reconstitution, how to calculate your draw volume, and how to store the solution correctly.

What Is Bacteriostatic Water?

Bacteriostatic water is sterile water containing 0.9% benzyl alcohol. The benzyl alcohol acts as a preservative — it inhibits bacterial growth without destroying the dissolved peptide. This is what separates it from plain sterile water.

Using plain sterile water for reconstitution is possible but means the solution must be used within 24–48 hours. With BAC water, a reconstituted peptide stored at 2–8°C typically remains stable for 4–6 weeks — enough for a full research cycle without re-reconstituting.

Why Not Sterile Saline?

Normal saline (0.9% NaCl) is isotonic and sterile, but like plain sterile water it contains no bacteriostatic agent. It can be used if BAC water is unavailable, but offers no shelf-life advantage. Some researchers use sterile saline for single-use preparations. For multi-week protocols, BAC water is the correct choice.

How Much BAC Water to Add

The volume of BAC water you add determines the concentration of your solution. The relationship is simple:

The most common choice is 1 ml because it produces the simplest mental math: the concentration in mg/ml equals the vial's mg value. A 5mg vial + 1ml = 5 mg/ml = 50 mcg per IU.

Common BAC Water Volumes and Resulting Concentrations

For peptides dosed in milligrams (e.g. Retatrutide 2–12 mg/week, Tirzepatide 2.5–15 mg/week), using 2–5ml of BAC water allows finer dose control at small draw volumes.

Step-by-Step Reconstitution Protocol

What You Need

• Lyophilised peptide vial
• Bacteriostatic water (3ml or 10ml vial)
• Insulin syringe (U-100, 1ml, 29–31G needle)
• Alcohol swabs
• Clean work surface

The Process

1. Bring to room temperature. Remove the peptide vial from the fridge 15–20 minutes before use. Cold powder can take longer to dissolve and is more prone to foaming if rushed.
2. Swab both stoppers. Wipe the rubber stopper of the peptide vial and the BAC water vial with separate alcohol swabs. Allow both to dry completely — 30 seconds is enough.
3. Draw BAC water. Insert the syringe through the BAC water stopper and draw your required volume (typically 1–2ml). Remove the syringe.
4. Inject down the glass wall. Insert the needle into the peptide vial and angle it so the BAC water streams slowly down the inside wall of the glass. Do not shoot it directly onto the powder cake — this can cause foaming and denaturation.
5. Gently swirl — never shake. Once all the BAC water is inside, gently rotate the vial between your fingertips. The lyophilised cake will dissolve within 30–60 seconds into a clear solution. If it appears cloudy after 2 minutes, continue swirling — do not shake.
6. Inspect the solution. A correctly reconstituted peptide is clear and colourless. Cloudiness, particles, or discolouration indicate a problem — do not use the solution.
7. Store immediately at 2–8°C. Cap the vial and place in the refrigerator. Do not freeze a reconstituted vial.

Calculating Your Syringe Draw

Once reconstituted, every dose requires drawing a precise volume from the vial. The formula:

The IU scale on an insulin syringe assumes 1 IU = 0.01 ml. This is consistent across all standard U-100 insulin syringes. The number you pull to on the syringe barrel equals your IU draw.

Use the free BAC Water Calculator for instant results — select your peptide, enter BAC water volume and desired dose, and it calculates concentration, mcg per IU, and exact IU draw automatically.

Storage After Reconstitution

• Temperature: 2–8°C (standard fridge). Never freeze a reconstituted solution.
• Duration: 4–6 weeks with BAC water. Some stable peptides (BPC-157, GHK-Cu) remain viable for up to 8 weeks; more fragile peptides (TB-500, growth hormone fragments) are safer to discard after 4 weeks.
• Light: Keep vials out of direct light. Store in the vial box or wrap in foil if storing long-term.
• Contamination: Always swab the stopper before each draw. Never draw air back into the vial from a used syringe.

Common Mistakes to Avoid

• Shooting BAC water directly onto the powder — causes foaming and peptide degradation. Always direct liquid down the glass wall.
• Shaking the vial — mechanical agitation denatures peptides. Swirl only.
• Using too little BAC water — very high concentrations can cause precipitation. 1ml per 10mg is a safe minimum.
• Reconstituting before needed — if you won't start a protocol for 2 weeks, keep the vial lyophilised. Reconstitute only when ready to begin.
• Using regular water — tap water and even distilled water are not sterile and introduce contamination risk.

Peptide-Specific Notes

BPC-157 (10mg): Add 1ml BAC water → 100 mcg/IU. Standard 500 mcg dose = 5 IU draw.

TB-500 (10mg): Add 2ml BAC water → 50 mcg/IU. Standard 2mg dose = 40 IU draw. Loading doses (5mg) require a 100 IU draw from a 2ml reconstitution.

GHK-Cu (50mg or 100mg): Add 5ml BAC water for 50mg vial → 10mg/ml = 1000 mcg/IU. Typical 1mg dose = 1 IU draw. For finer control, use 10ml BAC water (500 mcg/IU, 2 IU per 1mg dose).

Retatrutide / Tirzepatide: These are dosed in milligrams per week. Add 2ml BAC water to a 10mg vial → 5mg/ml. A 4mg weekly dose = 80 IU draw (0.8ml). Use a 1ml insulin syringe or a larger-bore syringe for these volumes.

Semax / Selank (10mg): Add 1ml BAC water → 100 mcg/IU. Typical 500 mcg intranasal dose = 5 IU. These peptides are frequently administered intranasally.

Frequently Asked Questions

How much BAC water do I add to a 10mg peptide vial?

Adding 1 ml gives a concentration of 10 mg/ml (100 mcg per IU) — the most common ratio for simple dose calculation. Use 2 ml for 50 mcg per IU if you need finer dose control at small volumes.

What is BAC water and why is it used for peptides?

Bacteriostatic water is sterile water containing 0.9% benzyl alcohol as a preservative. The benzyl alcohol prevents bacterial growth, allowing the reconstituted peptide to remain stable for 4–6 weeks refrigerated. Regular sterile water lacks this preservative — reconstituted peptides in plain sterile water must be used within 24–48 hours.

How long does a reconstituted peptide last in the fridge?

Most peptides reconstituted with BAC water remain stable for 4–6 weeks at 2–8°C. Lyophilised peptides before reconstitution can last 12–24 months at -20°C.

Can I use normal saline instead of BAC water?

Yes, but normal saline has no bacteriostatic preservative so the solution must be used within 24–48 hours. BAC water is strongly preferred for any multi-day protocol.

How do I calculate how many IU to draw for my dose?

Formula: IU = desired dose (mcg) ÷ mcg per IU. For a 10mg vial + 1ml BAC water: mcg per IU = 100. For a 500 mcg dose: 500 ÷ 100 = 5 IU. Or use our free calculator.