Using the formula above, I found that a single rainfall event of one inch would yield up to 1,300 gallons of water—if I had gutters and barrels all around my house to collect it. In Austin’s rainiest month of May, my roof could collect over 6,775 gallons. During an average year, that would be nearly 46,000 gallons.
However, I only have one gutter on my house, which collects water from less than one quarter of the roof. A single inch of rainfall would harvest about 280 gallons from that part of the roof. An average year would yield nearly 10,000 gallons from only that one part of the roof!
Just for kicks, I applied rainfall data from other regions of the state to see how my house would fare if it was whisked away and plopped down someplace else.
- In the Gulf Coast city of Port Arthur, my whole roof could collect over 8,700 gallons in June alone.
- In the desert of El Paso, my roof would collect over 12,000 gallons in a year of average rainfall.
Those numbers sound big, but what do those numbers mean, really?
If you fill a football field-sized (not including end zones) aquarium with water a foot deep, that will hold 47,000 gallons of water, or a little over one acre-foot. That’s close to my house’s annual rainwater harvesting potential!
A modern toilet uses 1.28 gallons of water per flush, which means my May yield would be enough to offset flushing the toilet nearly 5,300 times. Sometimes you need to flush more than once, right?