The polished metal vent pipe covers are for the black and gray tank vents.
They have nothing to do with the fresh water system.
Upon removing a cover, you will find the gasket cracked. The gaskets are cheap. When a new gasket is installed, a bead of vulkem sealer must be applied from the inner circle of the gasket, through the screening and on to the black pipe.
That gasket, depending on climate, lasts from about 4 years to about 10 years.