Compound file · Lab supplies
Bacteriostatic Water (BAC Water)
Bacteriostatic water is sterile water preserved with 0.9% benzyl alcohol, 0.22 µm filtered, intended for reconstituting lyophilised research peptides in multi-draw vials. It is the single most overlooked variable in reproducible peptide work.
- Composition
- Water for injection + 0.9% benzyl alcohol
- Filtration
- 0.22 µm sterile filtered
- Vial
- 3 ml multi-draw, tamper-evident cap
- Use
- Reconstitution of lyophilised research peptides
- Storage
- 2–30 °C, do not freeze, keep out of direct light
How it works (and how it differs from sterile water)
Benzyl alcohol at 0.9% is a bacteriostatic preservative: it inhibits bacterial growth rather than sterilising on contact. That inhibition is what makes repeated draws from the same vial acceptable over a working period, instead of forcing a single-use discipline.
Sterile water for injection contains no preservative. It is sterile at the moment the stopper is first pierced and offers no protection afterwards, so it is a single-draw diluent only. If your protocol draws from a reconstituted vial more than once, bacteriostatic water is the correct choice.
Benzyl alcohol is not inert for every molecule. A small number of peptides and biologics are documented as incompatible with preservative-containing diluents; check the compound's own literature before assuming bacteriostatic water is appropriate.
- Bacteriostatic = inhibits growth, enables multi-draw vials
- Sterile water = no preservative, single draw only
- 0.22 µm filtration removes bacteria at the point of manufacture
- Check compound-specific compatibility with benzyl alcohol
Using BAC water to reconstitute
Bring both vials to room temperature. Swab both stoppers with 70% isopropyl alcohol and allow them to dry — wet alcohol carried into the vial is itself a contaminant.
Draw the volume your target concentration requires, then inject it slowly against the inner glass wall of the peptide vial. The powder cake should dissolve on gentle swirling. Concentration is milligrams of peptide divided by millilitres of BAC water added.
- 10 mg peptide + 3 ml = 3.33 mg/ml
- 10 mg peptide + 2 ml = 5 mg/ml
- 50 mg peptide + 2 ml = 25 mg/ml
- Never spray diluent directly onto the powder; never shake the vial
Storage & shelf life
Unopened bacteriostatic water is stable at room temperature: store between 2 and 30 °C, out of direct sunlight, and do not freeze. Refrigeration is not required before first use.
Once the stopper has been pierced, treat the vial as a working consumable: keep it clean, capped and dated, and discard it at the end of the working period defined by your lab's protocol — commonly 28 days after first puncture. Discard immediately if the solution is cloudy or contains particulates.
- Unopened: 2–30 °C, dry, out of direct light
- Do not freeze — freezing compromises the preservative distribution
- Date the vial at first puncture and follow your lab's discard interval
- Discard on any cloudiness, discolouration or visible particulate
Lab handling notes
Use one fresh sterile needle per draw, and never re-enter the vial with a used needle. Keep the diluent vial away from the reconstituted peptide vials on your bench so lot labelling never gets confused.
Bacteriostatic water is a supply item, not a research compound — but it is still supplied for laboratory use only, not for human or veterinary administration.
BAC Water — frequently asked
What is the difference between bacteriostatic and sterile water?
Bacteriostatic water contains 0.9% benzyl alcohol, which inhibits bacterial growth and allows multiple draws from one vial. Sterile water has no preservative and is single-draw only.
How long is a vial good for after the first draw?
Labs commonly apply a 28-day working period after first puncture, provided the vial is kept clean, dated and free of cloudiness or particulates. Follow your own protocol's discard interval.
Can bacteriostatic water be frozen?
No. Freezing damages preservative distribution and vial integrity. Store between 2 and 30 °C.
How much do I need per peptide vial?
Divide the peptide mass by your target concentration. For example, a 10 mg vial at a 5 mg/ml target needs 2 ml of bacteriostatic water.
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Catalogue
Shop all research peptides
≥98% purity, batch-certified, 24h EU dispatch.
Educational information for qualified researchers. KUULPEPS compounds are supplied for laboratory research use only and are not medicines, food supplements or cosmetics. Not for human or veterinary consumption.