galvanized pipe (steel pipe with a Zinc Coating)
The old dairy farmer trick when the milk cooling compressor quit was to through silver dollars in the milk tank as the silver kept the somatic cell count down.
Many diary farmers use colloidal silver as a first line defense against mastitis.
Zinc is often hailed for its antiviral properties. Presuming the colloidal silver is a topical application. Colloidal silver taken internally has lasting, unsightly effects.
Hospitals use colloidal silver against bacteria as well. Its record for viruses, however, is apparently more mixed.