Place the barrel next to a downspout of your gutter. Although you can place the water tank anywhere, positioning it under a gutter means that it will fill up faster. Using the box cutter, cut the spout so that it ends about 6 inches above the barrel. Take the lid off the barrel and store for later.
Pull the netting tight over the barrel opening and staple it in place. Place the barrel under the downspout.
Check the barrel after heavy rain to see if it is nearly full. Clean the leaves off the netting and place these in your compost bin if you have one. When the barrel is full, place the lid on.
Fill your watering can from the barrel. If you have a barrel with a tap, you can draw the water without taking off the lid.