How Much Rain Water Will My Roof Collect

Rainwater collection calculation formulas and equations roof area ft2 x precipitation amount in x 0 623 amount collected gallons easy formula to remember.

How much rain water will my roof collect.

For example on a 2 000 square foot roof you can collect 2 000 x 0 56 1 120 gallons inch of rain. 0 623 gallons easy to remember formula. Just a half inch of rain falling on a 1 000 square foot roof will yield 300 gallons of water. John hickenlooper recently signed house bill 1005 which allows a maximum of two rain barrels with a combined capacity of 110 gallons are allowed at each household.

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. The measure is to take effect on aug. When you look at the numbers it s surprising how much water you can collect every time it rains. That s 600 less gallons you have to pay for and use from your town water supply.

So how can you do the math for your own roof. With over 600 gallons of high quality water available from a single inch of rain falling on 1000 square foot surface even an 85 collection efficiency estimated for clay tile will give you a lot of high quality water. If your average rainfall was 25 inches year your annual collection potential is 1 120 x 25 28 000 gallons year. Rain barrel supplies list.

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. Concrete tile may leave you with alkalinity in your water but this isn t necessarily a problem. 1 of rain on 1 000 sf roof will yield 623 gallons roof area m2 x precipitation amount mm amount collected liters. You can use the precipitation map below to find an approximate amount for your area.

This capacity can be calculated using the following formula. Keep in mind most rain falls over 2 3 months of a year. 1 of rainfall over 1 000 sf will yield 623 gallons to calculate the amount of rainwater you can collect you need to know your annual average precipitation for your area. 1 of rain x 1 sq.

Now most homeowners in the state are allowed to collect precipitation for later outdoor use. Roughly speaking 1 millimetre of rain over 1 square metre of roof equals 1 litre of water. To find how much rain you can collect in an average rain year multiply this number by the average inches of rain. Annual rainfall in millimetres x roof surface area in square metres roof catchment capacity.

To get an idea how much water the roof of your own house might yield use the rainfall harvest calculator above.