For folks who live in buildings were they are not allowed (by lease or renting) to have a permanent rainwater harvesting system. This video shows a fellow that has given this a lot of thought - it demos a pre-set tarp and a poles. When it rains, you would go out and set the tarp and add a bucket. Post-disaster, this would be a dandy way to gather rainwater, a real resource. Minimal cost, temporary and effective.
Brilliant! Going to buy the makings for one of these because the water that runs off my roof carries a heavy dose of moss-be-gone, bird crap and pine needles with it.
Most roofs, other than metal roofs, are unsuitable for water harvesting. Thought this might be of interest....