Using a copper cup is very healthy. It purifies blood. It removes toxins from body. It is good for skin, and heart. It reduces Kapha.
It is believed that to prevent Asthma, one should drink water which has been kept overnight in a copper vessel. This water, with traces of copper in it, is believed to change one’s constitutional tendency to get respiratory problems.
However, when using a copper cup, make sure that you rinse & scrub well during washing and ensure that there are no deposits or precipitates. Copper sulphate coating of unclean vessel can cause vomiting.