Peptide Reconstitution 101: BAC Water Ratios & Calculator

This guide is for research and educational purposes only.

Bacteriostatic Water vs Sterile Water

These two solvents serve different purposes, and choosing the wrong one can compromise your research.

Bacteriostatic Water (BAC Water)

Bacteriostatic water is sterile water containing 0.9% benzyl alcohol as a preservative. The benzyl alcohol inhibits the growth of bacteria, making it safe for multi-dose vials that will be punctured repeatedly over several weeks.

• Use for: Multi-dose research vials (the standard use case)
• Shelf life after reconstitution: 4-6 weeks refrigerated at 2-8°C
• Where to buy: Pharmacies, medical supply vendors, reputable peptide suppliers

Sterile Water (Water for Injection)

Sterile water contains no preservative. It is used when benzyl alcohol sensitivity is a concern or for single-use preparations.

• Use for: Single-use preparations only
• Shelf life after reconstitution: Use within 24 hours; discard remainder
• Limitation: No antimicrobial protection — each needle puncture is a contamination risk

For virtually all multi-dose peptide research, bacteriostatic water is the correct choice.

Standard Reconstitution Math

The goal of reconstitution math is to determine: (a) what concentration your solution will be, and (b) how much solution to draw for each dose. The formula is straightforward:

Concentration = Peptide Amount (mg) / Volume of Water Added (mL)

For example: 5 mg of BPC-157 reconstituted with 2 mL of BAC water = 2.5 mg/mL. If your target dose is 250 mcg (0.25 mg), you need: 0.25 mg / 2.5 mg/mL = 0.1 mL = 10 units on a 100-unit insulin syringe.

Skip the manual math entirely and use our Peptide Calculator — it handles reconstitution volumes, concentration, and dose-per-tick calculations automatically.

Common Reconstitution Ratios

The following table covers the most frequently used reconstitution ratios. These are not mandated — you can use any volume that gives you a practical per-dose measurement. The goal is a concentration that results in a reasonable volume per dose (typically 5-30 units on an insulin syringe).

Note: A standard 1 mL insulin syringe has 100 units. Each unit = 0.01 mL. Doses below 5 units become difficult to measure accurately with standard syringes — add more water to increase volume per dose if needed.

Step-by-Step Reconstitution Process

1. Wash hands thoroughly and work on a clean, flat surface. Wear nitrile gloves if available.
2. Gather supplies: peptide vial, bacteriostatic water, insulin syringe (or 3 mL syringe for drawing water), alcohol swabs.
3. Swab both vial stoppers — the peptide vial and the BAC water vial — with alcohol swabs. Let dry for 10 seconds.
4. Draw the calculated volume of BAC water into the syringe. Pull back the plunger past your target, then push forward to remove air bubbles.
5. Insert the needle into the peptide vial at a slight angle through the rubber stopper. Do not plunge directly onto the powder cake.
6. Inject the water slowly along the glass wall of the vial. Let it trickle down the side onto the peptide. Never blast the stream directly onto the lyophilized cake — this can damage the peptide structure and cause foaming.
7. Wait for dissolution. Most peptides dissolve within 1-3 minutes. You can gently swirl the vial to assist. Never shake the vial — shaking creates foam, denatures peptide at the air-liquid interface, and introduces microbubbles that make accurate dosing impossible.
8. Inspect the solution. It should be clear and colorless. If particles remain after 5 minutes of gentle swirling, there may be a solubility issue.
9. Label the vial with compound name, concentration (mg/mL), date reconstituted, and discard-by date.
10. Refrigerate immediately at 2-8°C.

Syringe Types and Measuring

For subcutaneous peptide research, insulin syringes are the standard tool. Understanding the markings is essential for accurate dosing.

1 mL Insulin Syringe (100 units)

• Total volume: 1 mL = 100 units
• Each small tick: 1 unit = 0.01 mL
• Each large tick (numbered): 10 units = 0.1 mL
• Needle gauge: typically 29-31G (thin, suitable for subcutaneous injection)

0.5 mL Insulin Syringe (50 units)

• Total volume: 0.5 mL = 50 units
• Each small tick: 1 unit = 0.01 mL
• Better for small doses — easier to read fine gradations

0.3 mL Insulin Syringe (30 units)

• Total volume: 0.3 mL = 30 units
• Best precision for very small doses
• Commonly used in clinical settings for insulin micro-dosing

Tip: If your calculated dose is less than 5 units, use a 0.3 mL syringe for better accuracy, or add more BAC water during reconstitution to increase the volume per dose.

Common Mistakes to Avoid

• Shaking the vial — Causes foaming, peptide denaturation at the air-liquid interface, and inaccurate dosing due to bubbles. Always swirl gently.
• Spraying water directly onto the powder — Can damage the peptide and cause clumping. Trickle down the vial wall.
• Using tap or distilled water — Neither is sterile. Only use bacteriostatic water or sterile water for injection.
• Forgetting to swab stoppers — Rubber stoppers are not sterile out of the package. Always alcohol-swab before puncturing.
• Leaving reconstituted peptides at room temperature — Refrigerate immediately. Even 30 minutes at room temp is wasted stability.
• Reusing syringes — Never reuse a syringe. Needle tips dull after one puncture, and reuse introduces contamination. Insulin syringes are inexpensive — use a fresh one every time.
• Not labeling vials — Multiple reconstituted vials in a fridge with no labels is a recipe for dosing errors. Label every vial.
• Reconstituting too much at once — Only reconstitute what you will use within the stability window. If you have a 10 mg vial and your protocol only needs 2 mg over 4 weeks, consider splitting into smaller aliquots.

For detailed compound-specific information, visit our compound guide index. For instant reconstitution and dosing calculations, use the Peptide Calculator.