Bacteriostatic Water for Peptide Reconstitution

Bacteriostatic water is sterile water containing 0.9% benzyl alcohol as a preservative. It is supplied in sealed multi-dose vials, most commonly 10 mL or 30 mL, and in laboratory peptide work it is the standard solvent for returning lyophilized (freeze-dried) material to solution.

The word bacteriostatic describes what the benzyl alcohol does: it holds bacterial growth in check rather than killing organisms outright. That distinction matters in practice. The preservative buys a vial a usable life measured in weeks instead of a single session, but it is not a licence to be careless at the stopper. It suppresses what might otherwise multiply; it does not sterilise what a contaminated needle introduces.

For a research bench, that multi-session window is the whole point. A 30 mL vial reconstitutes many peptide vials across weeks of work, and the alternative, discarding the remainder of a sterile water vial after every single withdrawal, is both wasteful and awkward to schedule around.

No. Unopened vials are held at controlled room temperature, around 20 to 25°C, away from direct light. Refrigeration adds nothing: the preservative does the work that cold would otherwise be asked to do, and cycling vials between cold storage and the bench encourages condensation on the stopper, which is the one surface you least want wet.

This is the point where the diluent and the peptide part company, and it is the source of most of the confusion. The reconstituted peptide generally does belong in the fridge, typically at 2 to 8°C, and for longer horizons the lyophilized powder belongs in a freezer. The water going in does not. Storing the water cold and the reconstituted solution warm is precisely backwards.

For the peptide side of that split, see the peptide storage guide.

Two clocks run, and the second one overrides the first.

Unopened, a vial typically carries a manufacturer shelf life of two to three years, printed on the label. Stored at room temperature in its carton, it is good until that date.

Once punctured, the working limit is 28 days. That figure is the conventional interval over which 0.9% benzyl alcohol is relied on to suppress growth in a repeatedly entered vial, and it starts at the first puncture regardless of how much volume was withdrawn. A vial with two years left on its printed date is still finished if it was opened 29 days ago.

Independently of both clocks, discard on appearance. Cloudiness, discolouration, visible particulate or a compromised stopper end the vial’s life immediately, whatever the dates say.

There is no fixed answer, and any source that gives you one without asking a question first is guessing. The volume of diluent added sets the concentration of the resulting solution, so it is derived from the concentration the protocol calls for, not from the vial.

The arithmetic is simply concentration equals mass divided by volume. A 10 mg vial brought up in 2 mL yields 5 mg/mL; the same vial in 1 mL yields 10 mg/mL. Larger volumes make small quantities easier to measure accurately and are generally preferred when the measuring instrument is the limiting factor. Working volumes of 1 to 3 mL per vial cover most laboratory handling.

Rather than work it by hand, use the calculators: the reconstitution calculator converts vial mass and target concentration into a diluent volume, and the bacteriostatic water calculator totals the diluent needed across a set of vials so you know how many to order.

Canadian researchers sourcing diluent domestically avoid the two problems that come with importing it: customs clearance on a low-value consumable, and transit times long enough to make restocking hard to plan. Volta ships from British Columbia, so Canadian orders move domestically without crossing a border.

Bacteriostatic water is a preserved diluent rather than a peptide, and Volta does not currently supply it — it is sourced separately, from a laboratory or medical consumables supplier. Sourcing it inside Canada rather than importing it is the practical advice here: it is a low-value, liquid consumable, which is the worst possible thing to have sitting in a customs queue.

For how the diluent fits with the rest of a working bench, see the equipment guide, and for the arithmetic of how much to add to a given vial, the reconstitution calculator.