This is how we collect and filter rainwater while living in a yurt on a permaculture farm.
If you're curious about the Big Berkey water filter we use, check out this article:
http://www.naturalnews.com/047373_Big_Berkey_water_filter_ProPur_lab_tests.html
You can get them here if you decide to buy one:
https://geni.us/BigBerkey