The USP 23 monograph states:
“Water for Injection (WFI) is water purified by distillation or re-verse osmosis.”
WFI is produced by either distillation or 2-stage RO. It is usually stored and distributed hot (at 80°C) in order to meet microbial quality requirements.
The USP monograph makes no references to bacteria limits for WFI. It does not need to be ster-ile; however, the monograph specifies that WFI not contain more than 0.25 USP endotoxin units (EU) per mL. Endotoxins are a class of pyrogens that are components of the cell wall of Gram-negative bacteria (the most common type of bacteria in water). They are shed during bacterial cell growth and from dead bacteria. Indirectly, the water must be of a very high microbial quality in order to have a low endotoxin concentration. The USP informational section recommends an ac-tion limit of 10 cfu/100 mL. The recommended method of testing is membrane filtration of a 100-mL sample and plate count agar at an incubation temperature of 30 to 35°C for a 48-hour period.
The chemical purity requirements of WFI are the same as PW.