A pump assembly for an emergency eyewash station and method of retrofitting a plumbed emergency eyewash station is disclosed. The pump is configured into two parts, an impeller assembly and a drive assembly, that are configured to couple together. The impeller assembly is isolated from the drive assembly and can be easily replaced to ensure a sterile fluid path is maintained for the eyewash fluid. The drive assembly can be fluid powered or an electric motor as desired. The present invention allows a plumbed eyewash station to be retrofitted to use a sterile eyewash fluid. The present invention can also be used in portable eyewash station units too.