CJK:
I wouldn't advise that unless you do not use sanitizers or have not for a couple months. Also, those with well water it also is a no go. That iron will play with your parameters forever, believe me. Also if your conditioning your water, you must watch for toxins from these compounds. If none of this applies to you, go for it!!!
Harry:
A stream??? Not where i'm from, your asking for pesticides, herbicides, and fertilizers to contaminate your rock. Yes, if you live in the foothills it would be a great way. But not a "normal" stream will be safe, you have to back-track into no-man's land for safety.
Just my $0.02
DW302