Voting Question: How to boil water while backpacking?

I will be on the trail for 3 to 4 days on a backpacking trip. I need a light weight solution to get clean water from streams. I don't want to invest in torch type gas boiler, I just want a good lightweight kettle to put directly on a fire. Anybody got any suggestions?
Is it common to put kettle directly on fire?
Thanks for the answers, but....

Like I said I don't want to invest in a gas/alcohol torch, I just want to use a campfire that we will be building every night anyways. Just a standard stainless steal kettle on open flame?

Source:
http://answers.yahoo.com/question/index?qid=20110131184904AAZx29m

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