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Step 1
Estimate the quantity of water you'll need for your garden in gallons of rainwater per month.
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Step 2
Calculate the available rainfall water supply for your rain barrel. Use the average inches of rainfall per month to calculate the gallons-per-month rainwater yield of your home's various roof surfaces. For every 1,000 square feet of roof surface, 1/2 inch of rain will produce 280 gallons of rainwater. To calculate rainwater yield more specifically, use the rainwater yield table (see Resources).
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Step 3
Use the smaller number of gallons in steps 1 and 2 to determine the size of rain barrel to purchase. Commercially-sold rain barrels range in size from 34 to 300 gallons.
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Step 4
Based on the location of your rain barrel (under which roof), as determined in step 2, select the specific design, shape, material and color of rain barrel that best fits the location. Consider size, appearance and location.
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Step 5
Decide which mechanism for accessing water from the rain barrel best fits your needs. Options include spigots, hoses, taps and rubber or wooden plugs. Choose the barrel that fits your requirement.
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Step 6
An overflow tube.Make sure the rain barrel has an overflow outlet that allows water in excess of barrel capacity to drain off in a controlled condition. Overflow hoses or pipes should be of sufficient length to feed into a drain pipe, or other water-runoff mechanism, that will carry the water away from the foundation of your house.
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Step 7
Make sure the rain barrel has a drain plug in the lowest part of the barrel so that stale water may be drained periodically, and silt and accumulated debris may be removed.
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Step 8
A wire insect cover.Make sure that the top of the rain barrel has a wire screen to prevent mosquito and other insects or trash from entering the barrel.
