Rainwater harvesting is the collection of roof runoff for domestic or irrigation uses. Capturing rainwater for later use converts rainwater to a natural resource that is otherwise treated as pollution when it enters the storm sewer system.

There are many forms of systems designed to capture and store rainwater. Rain barrels offer the average homeowner an easy affordable option.


How much rain water can you catch?

Puget Sound averages about 3 feet of rain per year, most of it falling between November to March.

Seattle's Monthly Average Rainfall in Inches

Jan

Feb

Mar

April

May

Jun

Jul

Aug

Sept

Oct

Nov

Dec

5.4

4.0

3.5

2.3

1.7

1.5

0.8

1.1

1.9

3.2

5.8

5.9

To determine the amount of rain your roof catches, multiply your home¡¯s width by its length (in feet) to estimate its footprint (ft2). Then, estimate the portion of this area that drains to the downspout you¡¯ll be using to catch your rain.

Rain Caught (gallons) = Footprint to downspout (ft2) x rain event (in) x 0.6*

Example:

  • Footprint of home = 1,000 ft2
  • Rain event = 1/4"
  • Approximately 50% of footprint goes to downspout

Rain caught = (1,000) x (.50) x (.25) x (0.6) =  75 gallons.

Note: Storage is limited to the capacity of your system. Added capacity helps your system weather the dry spells (See Photo Gallery for 'Double Barrel' configuration).

 

 *One inch of rain falling on a square foot of surface yields approximately 0.6 gallons of water.

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