The action level for Copper in drinking water is about 1.3mg/L, which is a high level, relative to other substances.
There are some people who have certain diseases like Wilson's disease, who have a difficulty regulating the amount of copper in the body, they are more seceptable to illness from high levels of copper.
If you're interested in reading the article, you scan view it here..
http://www.doh.wa.gov/ehp/dw/Contaminants/copper.pdf
-SF