Saving rain is imminently sensible. The Berkey would come in handy in the final stage for human consumption given what all actually runs off roofs everywhere(in terms of minute toxic particles). However, a couple of years ago the state of Washington was proposing taxing rain barrels(seriously). In many areas this is a business opportunity in waiting.

http://www.gardenwatersaver.com/9.html

http://www.cityfarmer.org/rainbarrel72.html

primarily specific to Texas(as an example):

http://209.85.207.104/search? q=cache:BHdISbjvFNIJ:http://www.cstx.gov/docs/rwh_suppliers_fall_2007.pdf+rain+water+savers,+canada& hl=en&ct=clnk&cd=6&gl=us&client=safari