Bacteriostatic Water Calculator
Bacteriostatic water (BAC water) is the standard solvent for reconstituting lyophilized peptides. This calculator determines the optimal amount to add for your desired concentration.
Bacteriostatic water contains 0.9% benzyl alcohol, which inhibits bacterial growth and extends the shelf life of reconstituted peptides to approximately 28-30 days when refrigerated. The amount of BAC water you add directly determines the concentration of your solution, which in turn affects how much volume you need to draw per dose. Adding more water creates a more dilute solution (easier to measure small doses) while adding less creates a more concentrated solution (fewer injections needed for larger doses). This calculator helps you find the sweet spot for your specific protocol.
How to Use
Enter the total milligrams of peptide in your vial as labeled.
Enter your desired dose per injection in micrograms.
Choose your preferred syringe volume to draw per dose (common choices are 0.05mL, 0.1mL, or 0.2mL).
The calculator outputs the exact volume of bacteriostatic water to add to achieve your desired concentration.
Use a separate sterile syringe to draw and inject the bacteriostatic water into the peptide vial.
Record the water volume added on the vial or in your research log for reference.
Formula
BAC Water (mL) = (Peptide mg x 1000) / (Desired mcg per dose / Desired mL per dose)Example
For a 5mg BPC-157 vial where you want 250mcg per dose at 0.1mL per injection: BAC water = (5 x 1000) / (250 / 0.1) = 5000 / 2500 = 2mL. Add 2mL of bacteriostatic water and each 0.1mL draw will contain exactly 250mcg.
Frequently Asked Questions
How long does bacteriostatic water last after opening?
An opened vial of bacteriostatic water is generally considered usable for up to 28 days when stored at room temperature or in the refrigerator. The benzyl alcohol preservative helps maintain sterility, but using a new vial monthly is recommended for optimal safety in research settings.
Can I use too much or too little bacteriostatic water?
Using too much water creates a very dilute solution that may require large injection volumes, which can be uncomfortable. Using too little can make it difficult to measure small doses accurately with standard syringes. A good rule of thumb is to aim for each dose to be between 0.05mL and 0.3mL on an insulin syringe.
Does the amount of bacteriostatic water affect peptide potency?
No, the amount of water does not change the total peptide in the vial or its biological potency. It only changes the concentration. Whether you add 1mL or 3mL to a 5mg vial, you still have 5mg of peptide total. You simply adjust the volume you draw per dose accordingly.