Bacteriostatic Water Explained
What Is Bacteriostatic Water?
Bacteriostatic water is sterile water with a small amount of a preservative added — specifically 0.9% benzyl alcohol. The word "bacteriostatic" breaks down as "bacteria" + "static" (meaning "held still"), so it literally means water that holds bacteria still. The benzyl alcohol does not necessarily kill every microbe, but it stops bacteria from multiplying. That means if a stray bacterium gets in while you are using the vial, it cannot grow into a colony and spoil the whole thing.
This matters because researchers often draw from the same vial several times. A preservative that keeps the water clean between uses makes it a practical, reusable solvent (a solvent is just the liquid you dissolve something into).
How It Differs from Sterile and Distilled Water
These three are easy to mix up, so here is the difference in plain terms:
Sterile water
Sterile means free of living microbes at the moment it was made. Sterile water is clean, but it has no preservative. Once you open it and start drawing from it, there is nothing to stop any microbe that wanders in from multiplying — so it is generally treated as single-use.
Distilled water
Distilled water has been boiled into steam and condensed back into liquid to remove minerals and impurities. It is very pure in terms of dissolved salts, but distillation does not make it sterile and it has no preservative — so it can still carry or grow microbes.
Bacteriostatic water
Bacteriostatic water is sterile and preserved with benzyl alcohol. It is the only one of the three that resists bacterial growth after opening, which is why it is the usual choice for a multi-use lab vial.
Why It's Used to Reconstitute Lyophilised Peptides
Research peptides are supplied as a lyophilised (freeze-dried) powder. To use one on the bench, a researcher must reconstitute it — mix the dry powder back into a liquid. Bacteriostatic water is a common choice for this in vitro step for two reasons: it is sterile, so it will not introduce contamination, and its preservative keeps the resulting solution cleaner for longer, which extends how long the prepared sample stays usable in the lab. Our reconstitution calculator helps work out how much water to add to reach a target concentration, and you can read the wider context in Peptide Storage & Handling.
Handling & Storage
As general lab practice, bacteriostatic water is stored at room temperature away from direct light unless the product label says otherwise. Wipe the rubber stopper with an alcohol swab before drawing from it, and use a clean tip or needle each time to avoid introducing contamination. Once a vial is opened, the preservative limits but does not permanently prevent spoilage, so an opened vial is commonly used within about 28 days — always follow the instructions on the specific product. Velox supplies bacteriostatic water for in vitro laboratory use.
Frequently Asked Questions
What is the difference between bacteriostatic and sterile water?
Both are sterile, meaning free of living microbes at the point of manufacture. Bacteriostatic water also contains 0.9% benzyl alcohol, a preservative that stops bacteria from multiplying if any are introduced. Plain sterile water has no preservative, so a single multi-use vial of bacteriostatic water can stay usable longer in the lab.
What is the shelf life of bacteriostatic water once opened?
As a general lab practice, an opened vial of bacteriostatic water is often used within about 28 days when stored as directed, because the benzyl alcohol preservative limits but does not permanently prevent contamination. Always follow the storage instructions on the specific product.
Why not use tap or distilled water to reconstitute peptides?
Tap and distilled water are not sterile and can carry microbes and impurities that contaminate or degrade a sample, ruining experiments. Bacteriostatic water is sterile and preserved, which is why researchers prefer it for reconstituting lyophilised peptides in vitro.
