Great if you can get at the main where it counts ! From bitter experience,this is not always possible.
Why are not all services brought to a common point when entering a house [as in a factory ],then there would be no arsing around looking for main switches,main valves,gas, ect,ect. Some valves I came across over the years would need Sherlock Holmes to find them.
As regards a little copper dust getting in your tea,have you any idea what your local counsel dumps in your water supply without you even knowing ? Better not even think about it !!