I ran across a great site tonight, it uses google maps and a simple roof tracing tool to give you a conservative estimate on how much rain water you could collect within a year.
My home came up to be able to collect 30,000 gallons just from rain water off my roof.
Last year my water usage was ~ 38,000 gallons with my garden doubling my overall usage. Meaning my overall yearly can be cut almost in half by just reusing greywater as my primary watering method for the garden.
What is exciting about this is that as I balance my water usage with my supply I see that I am going to be able to have a surplus of available water, which I will discuss how I plan to achieve this – those of you doing the math right now realize that is about: qty 120 of 250 gallon containers, qty 545 of 55 gallon drums. Astounding yes I know, how to contain all of this, staggering concept and yet I will get into how this is achievable as we get into the grey water and rain collection systems later in the year. Have fun with this for now.