Bacteriostatic water (often shortened to BAC water) is one of the most common supplies in a peptide research lab. It looks like plain water, but it is formulated differently from sterile water, and that difference matters for how it is used and stored.
What it contains
Bacteriostatic water is sterile water that contains a small amount of benzyl alcohol, typically 0.9%, as a preservative. The benzyl alcohol does not sterilize anything. It inhibits the growth of most bacteria that might be introduced when a vial’s stopper is punctured, which is what “bacteriostatic” means.
Bacteriostatic water vs. sterile water
- Sterile water has no preservative. It is intended for single use: once the vial is opened, any leftover is typically discarded.
- Bacteriostatic water contains a preservative, so a vial can be entered more than once over a limited period. This makes it practical when a lab needs to draw small amounts from the same vial repeatedly.
- Because of the benzyl alcohol, bacteriostatic water is not interchangeable with sterile water for every application. Check the requirements of your protocol and any compatibility notes for the material you are working with.
Why labs use it with lyophilized materials
Many research peptides are supplied lyophilized, meaning freeze-dried into a powder for stability during storage and shipping. Before a lyophilized material can be used in most experiments it has to be dissolved in a suitable diluent. Bacteriostatic water is a common diluent choice in research settings because of its multi-use convenience. The correct diluent and volume depend on the material and the experiment, so always follow your own laboratory procedures.
Storage and handling
- Store unopened vials at controlled room temperature, away from direct light, unless the supplier label says otherwise.
- Wipe the stopper with alcohol before each entry and use a new sterile needle every time.
- Label opened vials with the date first entered. Multi-use vials are generally discarded within a limited window after first use; follow the label and your lab’s policy.
- Discard any vial that looks cloudy, discolored or contains particles.
Sizes we carry
406 Peptides stocks BAC Water in 3 mL, 10 mL and 30 mL vials. Smaller vials suit single experiments; larger vials reduce cost when a lab works through many samples. Confirm the formulation, preservative concentration and handling instructions on the supplier label of the vial you receive.
All 406 Peptides products are sold for laboratory research use only. They are not for human or veterinary use, and nothing in this article is medical advice.