How much bacteriostatic water do I add?

The most asked question we get, and the answer is not a single number. Here is what the volume actually changes, and the conversions people get wrong.

This is by far the most common question we get, and it is almost always the same misunderstanding: people assume there is one right amount of bacteriostatic water for a vial. There isn't.

What the volume actually does

Adding more water spreads the same amount of peptide through more liquid. That makes each marking on the syringe represent less peptide, which can make small measurements easier to read accurately. Adding less water concentrates it, so each marking represents more.

A 10mg vial, at different volumes

“Units in the vial” is the whole volume of liquid measured in insulin-syringe units. 1ml is 100 units on any insulin syringe, so divide that total by the units you draw each time to see how many draws the vial gives you.

Units versus millilitres

This trips people up constantly. Insulin syringes are marked in units, not millilitres, and the two are not interchangeable numbers. A unit is the same on every insulin syringe, so these conversions hold whatever syringe you use:

How to reconstitute

1. Let the vial come to room temperature. Cold glass and cold powder dissolve poorly.
2. Wipe both stoppers, peptide vial and water bottle, with an alcohol wipe.
3. Draw your chosen volume of bacteriostatic water.
4. Angle the needle so the water runs down the inside wall of the vial. Do not fire it straight onto the powder.
5. Swirl gently until clear.
6. Refrigerate once reconstituted.

Common questions

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

There is no single correct volume. The amount of water you add sets the concentration, not the quantity of peptide, the vial contains 10mg either way. Adding 1ml gives 10mg per ml; adding 2ml gives 5mg per ml. Choose the volume that makes your measurements convenient for the syringe you are using.

How many units is 1ml of bacteriostatic water?

1ml is 100 units. A unit is the same on every insulin syringe, so 0.25ml is 25 units, 2ml is 200 units and 5ml is 500 units whatever syringe you use. Evra supplies 1ml insulin syringes, marked to 100 units.

What is bacteriostatic water?

Sterile water containing 0.9% benzyl alcohol, which suppresses bacterial growth. That preservative is why it can be used across multiple draws from the same vial, unlike sterile water for injection, which has no preservative.

Can I use normal water or saline?

No. Tap or distilled water is not sterile, and plain sterile water has no preservative, so it is single-use only. Bacteriostatic water is the standard choice for a vial that will be accessed more than once.

How long does bacteriostatic water last once opened?

Manufacturers typically state 28 days once the stopper has been pierced. Keep the bottle at room temperature, not in the fridge, and check the label on the bottle you received.

Do I store bac water in the fridge?

No. Keep your bacteriostatic water at room temperature, below 25°C and out of direct light. Cold bac water can make peptides go cloudy or gel-like when you mix them. Once a peptide has been mixed, that vial does go in the fridge.

How do I add the water without damaging the peptide?

Draw the volume you want, then let it run slowly down the inside wall of the vial rather than firing it directly onto the powder. Swirl gently until dissolved.