How long can drinking water be stored in a copper vessel? 



First of all copper vessels should be cleaned every day. Because copper reacts with the oxygen in the air and oxides of copper is formed on the surface of vessel. The black bluish discoloration on the vessel. This oxides are poisonous to health.




New’ water, with its bonus of fresh aeration, should be added nightly, to maintain freshness of taste.





I don't have any documentation, but my own experiences with having copper pipe make me believe that clean water could be stored in copper vessels indefinitely, and remain safe for drinking.

Water in copper vessels should be kept only for 12 hrs. After 12 hrs that water should be consumed and fresh water should be added.

So it should be cleaned both internally and externally.