Well, there shouldn't be much, if any, contamination in rain water. But, if you're storing it in big drums like we're talking about in this thread, then you run the risk of critters getting in while it's sitting waiting for use. If it's fresh, I'd probably drink it, but if it's been sitting for any length of time, I'd treat/boil it to be safe. If you get into a situation where you're needing that water, you really don't want to get sick. <img src="/images/graemlins/blush.gif" alt="" />
-Kyle