Re: a copper cored hookah stem?
Brass can have a orange-ish gleam to it depending on the quality/series of metal. Only way to really know is a scratch test and/or if you can get a picture of the weld. Brass and Copper when welded use a similar types of filler material, but when brazed cool to a different tone.
There are alot of theories to the uses and safety of copper. FDA did a testing and research on cooper, I can go back and find it. There is alot of speculation if it safe for not, scientist and doctors alike are constantly studying its health effects. Problem is with copper, it can effect you differently depending on the quality of it, unlike most metals. I honestly wouldn't smoke out of copper until FDA or some one else with backing releases something solid on it. My opinion, I don't think its safe. There has been no true long term studies on using copper to smoke. I just know a few guys in our shop that fabricated a cigar pipe out of copper tubing and got really messed up with metal poisoning.
As for houses, they still use nickel-copper pipes for water and gas. PVC is mainly used for drainage.