Preparing the Area
Choose a spot for your rainwater harvester. The best place is next to the downspout where most of the water from your roof is diverted.
Level the ground, using a shovel and a garden rake, in the area where you'll place your storage tank.
Place flat landscaping rocks on the ground where the storage tank will sit, making sure they are level. The barrel will sit on the rocks, making it higher than the bottom hose or spigot, so gravity will pull the water down and out.
Preparing the Downspout
Place a debris screen inside the gutter at the downspout to keep pine needles, leaves and other debris from flowing into your water tank, recommends GutterWorks.com.
Install a water diverter by pulling the downspout off the gutter and screwing the diverter in place of it, using a screwdriver and gutter screws.
Trace the shape of the diverter onto the downspout using a marker.
Cut the downspout at the trace marks, using the metal snips, then reattach the downspout to the diverter, using a screwdriver and gutter screws.
Hook a hose to the outlet on the side of the diverter. Attach the other end of the hose to the inlet on the storage tank.