Laboratory reference
Bacteriostatic water
What it is, how it differs from sterile water, and why it is the liquid used to bring lyophilised research material back into solution.
Definition
What it is
Bacteriostatic water is sterile water containing a small amount of a preservative, usually benzyl alcohol at around 0.9%. The preservative inhibits bacterial growth, which is the whole reason it exists: it allows a sealed vial to be entered more than once instead of being discarded after a single preparation.
In a research setting it is used to reconstitute lyophilised compounds. The powder is stable for long periods dry, and considerably less stable once it is in solution, so it is dissolved only when it is needed and in a liquid that will not spoil between draws.
How it differs from sterile water
| Bacteriostatic water | Sterile water | |
|---|---|---|
| Contains a preservative | Yes, benzyl alcohol at roughly 0.9% | No |
| Suitable for repeated draws | Yes, the preservative inhibits bacterial growth between draws | No, treated as single use |
| Typical shelf life once opened | Commonly stated as up to 28 days | Discarded after one use |
| Usual laboratory use | Reconstituting lyophilised material that will be drawn from more than once | Single preparation, then discarded |
| Storage after opening | Refrigerated, sealed, away from light | Not applicable |
Reconstitution, step by step
- 01
Let the vial reach room temperature
Lyophilised powder taken straight from cold storage should be allowed to equilibrate before liquid is introduced. Cold glass and condensation both work against a clean preparation.
- 02
Clean both stoppers
Wipe the rubber stopper on the powder vial and on the water vial with an alcohol wipe and let each dry. The stopper is the only barrier between the contents and the room.
- 03
Draw the volume you intend to use
Volume determines the concentration of the resulting solution, so it should be decided and recorded before drawing, not adjusted afterwards.
- 04
Introduce the liquid down the vial wall
Directing the stream against the inside wall rather than straight onto the powder reduces foaming. Peptides are fragile in solution and agitation degrades them.
- 05
Swirl, never shake
Rotate the vial gently until the powder has dissolved. Shaking denatures peptide material. If it does not dissolve readily, more time usually works better than more force.
- 06
Label and refrigerate
Record the compound, the volume added, the resulting concentration and the date. An unlabelled reconstituted vial is unusable data a week later.
The reconstitution calculator works out the volume needed for a given concentration.
Common questions
What is bacteriostatic water?
Bacteriostatic water is sterile water containing a small amount of a preservative, usually benzyl alcohol at around 0.9%. The preservative inhibits the growth of bacteria, which is what allows a vial to be entered more than once rather than being discarded after a single use.
What is the difference between bacteriostatic water and sterile water?
Sterile water contains no preservative and is treated as single use: once the seal is broken there is nothing preventing bacterial growth. Bacteriostatic water contains a bacteriostatic preservative, so it can be drawn from repeatedly over a period commonly stated as up to 28 days when kept refrigerated and sealed.
Why is bacteriostatic water used to reconstitute research peptides?
Research peptides are supplied as a lyophilised powder and must be dissolved before they can be handled in solution. Bacteriostatic water is used where the resulting solution will be drawn from more than once, because the preservative limits bacterial growth in the vial between draws.
How long does bacteriostatic water last once opened?
A period of up to 28 days is commonly stated for a bacteriostatic vial once its seal has been broken, provided it is kept refrigerated, sealed and out of direct light. The unopened vial has its own expiry date printed on the label, which is separate and longer.
How should bacteriostatic water be stored?
Unopened vials are stored at room temperature away from direct light. Once opened, a vial is kept refrigerated and sealed. The stopper is wiped with alcohol before each entry, because it is the only barrier between the contents and the surrounding air.
What size vial is normally used?
A 3ml vial is the common size for research use, because it is enough to reconstitute several vials of lyophilised material while still being consumed within the period the preservative is effective for. Larger vials are more likely to expire before they are finished.
Supplied in the UK
Sealed 3ml vials, dispatched from the UK.
Last reviewed
For in vitro laboratory research use only. Not for human or veterinary use. This page describes laboratory handling practice and is not guidance for any other purpose.