Saved the best for last:
http://www.builditsolar.com/Projects/Water/Water.htm

Otherpower is about wind, not going to get much response on other subjects.
I have read everything linked to above. I would say I am book smart on rainwater.
Cistern when a kid, collect rain to water my batteries.

Not found a water diversion device I like (or willing to pay for), designed my own, which I do not like yet. Love to see anything you can come up with...

I live in Michigan, with a 2000sqft home a 2500gal tank for family of 4.
Sister in NM, would need 5000gal tank, same yearly rain fall. NM has no rain for months.
Made a spread sheet to calculate tank size based on monthly rain fall. I used the low numbers to calculate, not willing to run out of water!

Found plastic tanks for 2500 gal cost $1000 or so with shipping.
Ebay item 250237686170

Then came across the idea of digging a hole or a wood tank.
Line it with EPDM pond liner (60mil) about $1sqft, much less $ then the tank.
May be a problem for code and flooding considerations. So have top above ground.
Need a cover. How about a deck? Same idea works for solar heated tank.

Estimated it would cost $2k to use rain to replace a $8k well. Looks like a good deal, gave me the $ needed to do solar heating! Got laid off, building is on hold.
I can drive a shallow well for few hundred $, use for watering lawn.