BAC water vs sterile water

Two clear liquids in two identical-looking vials, sold beside each other, at similar prices. They are not interchangeable, and the difference is a single ingredient.

The difference in one line

Bacteriostatic water is sterile water with 0.9% benzyl alcohol added. Sterile water has nothing added.

That is the entire chemical difference. Everything below follows from it.

What the benzyl alcohol is doing

Benzyl alcohol is a bacteriostatic preservative: it stops bacteria multiplying in the liquid. It does not sterilise anything — the water was already sterile when it was sealed. What it does is protect the contents of the vial from what gets introduced the second, third and tenth time a needle goes through the stopper.

That is why bacteriostatic water is sold as a multi-draw vial. The preservative is what makes going back to the same vial a designed use rather than an accident.

What sterile water is for

Sterile water carries no preservative, so nothing is protecting it once the seal is broken. It is packaged for single use: open it, use it, discard the remainder. Keeping a part-used vial of sterile water and returning to it later is the failure mode the preservative exists to prevent.

Which one you need

The label on whatever you are reconstituting states which diluent it takes. That label decides it, not us, and not a guide. Some materials are specified with a preservative and some are specified without one, and the reasons are specific to the material.

PepCrate sells supplies. We do not supply, recommend or advise on anything that gets reconstituted, and we cannot tell you what your material calls for.

Reading the vial in front of you

Four things are worth checking before a vial goes in a case:

• The name. "Bacteriostatic Water" and "Sterile Water" are different products. A vial that says neither is neither.
• Multi-draw or single-use. It will say. It follows from the preservative.
• The volume. 10ml and 30ml vials have different diameters, which is why case slots are cut for a size. Ours are listed in millimetres on every product page.
• The date. Both the printed expiry and, once you open it, the date you opened it.

After it is open

Store it as the label says, upright, and dated. A part-used multi-draw vial is still a vial with a punctured stopper, and it belongs in a slot with the rest, not loose in a drawer. The storage guide covers the rest of it.

What we sell

We stock bacteriostatic water in two sizes: 10ml and 30ml. Both are sterile water with 0.9% benzyl alcohol for laboratory reconstitution of lyophilized research materials, multi-draw vial.

We do not stock sterile water.