I'd probably turn on my outside spigot for my wort chiller...I just have to make sure I turn it off when I'm done.
Once you turn the water on, I wouldn't turn it off until you're finished. Trust me, a frozen chiller is no fun.
I won't be brewing outside until spring (no way am I shoveling seven feet of snow off the porch) but last weekend I got the bug and did a partial boil on the stove. http://seanterrill.com/2011/01/16/of-ice-and-10p/