Learn how to purify water with the sodis method.  Even though I already knew you could purify the water this way, I did not know that even if you have boiled the water before storing, it can still be contaminated. Everyone  should read and know this.

http://www.sodis.ch/methode/anwendung/index_EN

Here is a really in depth article about it. 1,000 Bottles of Water on the Roof, by James C.