Yes, copper is toxic and can lead to many diseases. Just google it and you will know. Just because something is occuring in nature does not mean you should use it anytime and anywhere. Just think, if people after you will want to grow vegetables in this place? Is it really necessary to use chemicals to protect some sickly lilies?

The link below illustrates copper toxicity:

Here is a link that might be useful: What can copper make damage to

As with anything, it is all a matter of dosage - drink enough water and it can kill you too.

Here is a link that might be useful: a more reasoned approach to copper fungicides

I would still recommend drinking unpolluted water. It is extremely rare somebody dies because of drinking pure water. Poisoned water is not good to drink for anybody. I do not have a link to support it, so you choose yourself if you believe it or not.