This webinar has good information. It is about "understanding FEMA & Red Cross recommendations for treating water in an emergency. The webinar is on www.survivalstill.com.
The three main ways that it lists are:
boiling, chlorination and distilling. Distillation is the best out of the three. The host Glen Meder has created his own "survival still." It looks like a good product. It meets Fema & Red Cross recommendations and is made in the USA.
I need to get me one and build myself a rainwater catchment system.