I divert all the house rain gutters to rain barrels for garden water
and it keeps the electric bill down (we have an electric pump to a
private well). Just 3/4 inches of rain can fill each of 3 40-gallon
trash barrels. The water isn't pretty so it only goes to the garden
and peach tree. Any excess runs over the barrel and into irrigation
ditches which I dug into the garden. Last year we had a drought,
about one small thunderstorm every 3 to 4 weeks...so every drop
counted.

I'll be redirecting our downspouts here soon as well. The house has a
typical pitched roof as well as a small roof on an add-on (only a couple
hundred square feet). From what I've read, the typical home can capture
enough rainfall on the roof to account from a large chunk of the typical
water usage a 2 or 3 family needs in a year. Some interesting numbers. I'm
also looking into water purification systems -- would be nice to grab the
runoff from the roof and bring it into the house for things like laundry,
toilets, showers, and so forth.

James