1. Choose a rain barrel made with food-grade plastic that holds at least 55 gallons of water. Locate it uphill from the area you’d like to irrigate, near a downspout, and on a hard, flat surface. You can increase the water pressure coming from your rain barrel by elevating it on cinder blocks. To create a cinder-block base, place three 8-by-8-by-16-inch cinderblocks lengthwise (flat surface down, holes pointed out) and arrange them so they form a triangle. Check to make sure the blocks are level and then center the rain barrel on top of the base.
2. Select a front side for your barrel and attach a 3/4-inch spigot about 2 inches from the bottom using a bulkhead fitting. Reach down into the barrel to determine the lowest spot you can position the fitting, and drill a hole in the outside of the barrel. Thread the spigot into the fitting (using a reducer, or bushing, if necessary) so you get a tight, leak-free fit. “Use a spigot with a 3/4-inch male inlet, rather than a 1/2-inch one, because it allows more water to flow through, which is especially important if you plan to hook a soaker hose up to the barrel,” says Lenny Librizzi, who has installed 40 rainwater-harvesting systems for community gardens (including a couple as part of the Organic Gardening WaterWorks project) in his work for the Council on the Environment in New York City.
3. Prevent your rain barrel from overflowing by installing a downspout diverter. This simple system attaches to your downspout and allows you to divert water into the barrel. When it is full, water is redirected to your downspout.