22 December 2011

Home Rainwater Collection System: First Rain


Last night's rainfall filled up both of our 200 gallon tanks, with the overflow of one going to a 1,500 gallon tank. Wunderground lists total rainfall as 0.59 inches for this area. Not bad for the first collection, though we still want to add a couple more 1,500 gallon tanks to the system.


This got me wondering how much rain we can actually collect. Here is the formula:

Rainwater collection from roofs can be calculated using the following formulas:
  • 1 inch of rain on a 1000 square feet roof yields 623 gallons of water; or
Helpful Rainwater Collection Formula


We added on a 700 sq ft addition, making the total near 1,500 sq ft of roof that collects into this system. So, the math on that would be 1,500 X 623 / 1,000 = 934 gallons collected from 1 inch of rainfall for our system. Eventually the front of the house will be added to the system. We are too close to the Austin metro to drill a well, so this is the next best thing.

Since last night's rainfall was only 0.59, the math would be 0.59 X 934 = 551 gallons. Not bad at all. Even with the cost of a couple more 1,500 gallon tanks, this is still very practical, with the current setup saving enough money to pay for itself in a couple of years.

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