The Full Form of WFI is‍ Water for Injection.

Sterile Water for Injection, USP, is sterile, nonpyrogenic, distilled water in a single dose
container for intravenous administration after addition of a suitable solute. It may also be
used as a dispensing container for diluent use. No antimicrobial or other substance has
been added. The pH is 5.5 (5.0 to 7.0). The osmolarity is 0.
The VIAFLEX plastic container is fabricated from a specially formulated polyvinyl
chloride (PL 146 Plastic). The amount of water that can permeate from inside the
container into the overwrap is insufficient to affect the solution significantly. Solutions in
contact with the plastic container may leach out certain chemical components from the
plastic in very small amounts; however, biological testing was supportive of the safety of
the plastic container materials.