Cast iron fittings up to and including 51mm in size, when used in connection with potable water piping shall be_____.

Cast iron fittings used in connection with potable water piping must be galvanized to ensure they are suitable for carrying drinking water. Galvanization involves applying a protective zinc coating to the cast iron to prevent corrosion, which is crucial for maintaining water quality and safety. This coating protects the metal from rust and deterioration that could introduce harmful substances into the potable water system.

Welding or soldering these fittings is not appropriate for connection with potable water, as these methods may introduce contaminants or create seams that can corrode and leak over time. Anodizing, which is a process primarily used for aluminum and its alloys, does not apply to cast iron fittings in this context. Therefore, galvanizing is the best choice to ensure the durability and safety of the water supply system.