Bacteriostatic water: what it is

What bacteriostatic water is

Bacteriostatic water is water with a small amount of benzyl alcohol added. The benzyl alcohol slows the growth of bacteria. Because of this, the water can be used over a longer period after opening than water without an additive. In laboratory chemistry it belongs to the preserved aqueous auxiliaries.

The role of benzyl alcohol

Benzyl alcohol is the additive that gives the water its name. It is usually present at around 0.9 percent. Its job is to hold back the growth of micro-organisms. It does not sterilise the water on the spot. Instead, it keeps new bacteria from multiplying quickly once the container is open.

Difference from sterile water and saline

Plain sterile water contains no preservative, so once opened it is usually meant for single use. Bacteriostatic water contains benzyl alcohol, so it keeps for a limited period after opening. Saline is different again: it is water with salt added, and it does not by itself slow bacterial growth unless a preservative is also present.

Why the label says bacteriostatic

Bacteriostatic means growth-slowing, not killing. A bacteriostatic additive holds bacteria back rather than destroying them outright. That is why the water is called bacteriostatic and not, for example, bactericidal, which would mean bacteria-killing.

General handling in the lab

General handling follows the label. Bacteriostatic water is usually stored cool, dark, and closed. After opening it stays usable for a limited period, often a number of weeks, as stated on the label. Once that period has passed, it is discarded. Always follow the storage and shelf-life details on the product itself.