Friday, May 21, 2010

Collecting water from your roof

Ask Ida


Dear Ida B. Green,

Although it's been a fairly dry spring, I'd like to try rain barrels. How much could I collect off my 2,000-square-foot roof?

Signed,

Dry

Dear Dry,

Collecting rainwater for your garden is a smart idea, since plants prefer rainwater, which is naturally soft and free of chlorine. Additionally, you can save a bit on your summer watering costs and enjoy the convenience of having rain barrels close to frequently watered beds, flower pots or trees.

To roughly calculate the amount of water you might expect from your roof, multiply the area of your roof, times feet of rain, times 7.5. For your roof, this is 2,000 X .083 feet X 7.5 = 1,245 gallons of rainwater. Although some of this will be lost to evaporation, prevailing winds, and tree cover, you can count on collecting 75-85 percent of the total rainfall.

As the typical rain barrel is 55 gallons, this could have filled around 22 barrels in one rainfall, so unless you plan on constructing a larger holding tank system, it's a good idea to have overflow hoses, at least 5 inches below your barrels' top rim, and leading to nearby areas that can use a bit more water. I like to lay the hoses from each of my barrels to my fruit trees, which can always use considerably more rain than we typically get.

Easy to be Green,

Ida




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