Can copper vessel be boiled?

There is a possibility of corrosion. Any copper ions in drinking water are bad. Copper is generally toxic ; it is used to keep ship hulls free of barnacles , etc. That is why old copper pans are tin coated and new copper pans are clad with stainless steel ( I have recently seen new pans with an apparent tin coating ). The corrosiveness of the water depends on its composition , city water in plumbing is relatively benign. But when you add foods, many contain acids, etc ,that can release copper ions( corrosion), so bare copper cookware would be risky. Your water may pick up a trace of copper , and over time it could reach a harmful level in your body.

For a recurrent use in the kitchen, copper must be lined. This is done since long time. If you boil water for a safer consumption or to reduce the smell of disinfectants*, then definitely you should buy a copper boiler only if lined.

*otherwise don't boil it.