Water is an important aspect to all life on earth. Even the human body is made up of 60% water. This fact makes it easier for doctors and other healthcare specialists to administer drugs directly into the human body.

This is achieved by dissolving the drugs in water; preparing a solution of the drugs and administering it via injections and other intravenous mediums. Hence, it becomes imperative that we use water that is purified using appropriate processes.

We define the water that is used for these processes as Water for Injection or WFI. Thus, WFI can be defined as water that is used in the manufacture of parenteral (injectable) drugs whose solvent is water. The United States Pharmacopeia (USP) defines this as a highly purified water containing less than 10 CFU/100 ml of Aerobic bacteria.

WFI has stricter bacteria controls than purified water and hence the USP mandates these waters should have less than 500 ppb of total organic carbon, fewer than 0.25 EU/ml endotoxins, and a conductivity of less than 1.3 uS/cm @ 25 C.