To get an idea how much water the roof of your own house might yield use the rainfall harvest calculator above.
How much rain collected from roof.
To find how much rain you can collect in an average rain year multiply this number by the average inches of rain.
Rain barrel supplies list.
If your average rainfall was 25 inches year your annual collection potential is 1 120 x 25 28 000 gallons year.
Gallons collected per inch of rainfall 0 62 total collecting area of roof in square feet so if you have a 1 000 square foot house you can potentially collect 0 62 1 000 620 gallons of water every time it rains an inch.
Rainwater collection calculation formulas and equations roof area ft2 x precipitation amount in x 0 623 amount collected gallons easy formula to remember.
If you have 1 000 square feet of roof on your house and it rains just 1 inch you can collect 600 gallons of water to be used in your garden for washing your car or just for drop irrigation around your property.
With two inches of rain you can collect around 1 240 gallons.
For example on a 2 000 square foot roof you can collect 2 000 x 0 56 1 120 gallons inch of rain.
An average suburban roof of 200m 2 with such a rain fall can potentially harvest 100 000l of rainwater 200m 2 500mm 100 000l.
Just a half inch of rain falling on a 1 000 square foot roof will yield 300 gallons of water.
It isn t uncommon for an area to collect up to 350mm of rain in just one month even in rural areas.
So how can you do the math for your own roof.
Keep in mind most rain falls over 2 3 months of a year.