Thank you both for the links, I'll have to go through them.

One thing I have noticed about discussions on rainwater harvesting is that people are worried (possibly excessively) about contamination, automatically comparing it to what they think comes from their tap. They don't seem to realize that most municipal water supplies aren't providing pure water. Even chlorinated tap water isn't perfect, it simply reduces pathogens and contaminants to what is considered a safe level.

For instance, here are the test results for Los Angeles (2010)

It shows that there are still fecal coliform bacteria in the water. It shows that there is still Acrylamide, Epichlorohydrin, Aluminum, Arsenic, Barium, Nitrates, Radionuclides (like uranium), plus the stuff they add to disinfect the water: Trihalomethanes, Haloacetic Acids, Chlorine, Bromate.

The bottom line with rainwater harvesting is that it can be the difference between having water and not having water. If you store water, great. With rainwater harvesting you can bathe and wash clothes. If the disaster is extensive and you run out of your stored water, you've still got options.

Sue