Reconstitution & Vials
Bacteriostatic Water
Also called: BAC water, bacteriostatic water for injection
Definition
Sterile water for injection that contains an antimicrobial preservative intended to inhibit bacterial growth after entry into the vial.
What Bacteriostatic Water means
Bacteriostatic water is commonly shortened to BAC water. In calculator math, the relevant input is the liquid volume added to a vial because that volume determines concentration.
Why the distinction matters
BACToBasics treats BAC-water calculations as arithmetic and educational context, not as instructions for preparing or using a medication or research compound.
Common confusion
Bacteriostatic water and sterile water are not interchangeable labels. The presence or absence of an antimicrobial preservative is an important distinction.
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Open the BACToBasics tools and reference pages where this term is used.
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Related glossary terms
Reconstitution & Vials
Sterile Water
Sterile water for injection that does not contain the bacteriostatic preservative found in bacteriostatic water.
Reconstitution & Vials
Reconstitution
The process of adding a liquid to a dry or lyophilized product so that it becomes a solution or suspension with a calculable concentration.
Math & Measurement
Concentration
The amount of a substance contained in a given volume of liquid, such as mg/mL or mcg/mL.
Math & Measurement
Milliliter (mL)
A metric unit of liquid volume equal to one-thousandth of a liter.
Published September 6, 2026. BACToBasics glossary pages are educational definitions only and do not provide medical, dosing, preparation, treatment, or product-selection advice.