You need a fairly large container to collect the water when it comes down the spout from your gutters. A 55-gallon barrel or cistern is all you need to hold enough water for watering your lawn and garden or to wash your car. You can buy specially designed containers for collection; these containers come with outlets for hoses and for filling watering cans. To save money though, you can make your own container out of a polyethylene, fiberglass or metal barrel or drum, which is what this project will focus on.
Only use containers meant to hold water or food. Don't use any container that once held chemicals.
Never use the water collected for drinking.
Check with your local municipal officials to make sure it is legal to collect and hold water for reuse.
Place your rainwater container on concrete cinder blocks near where your gutter downspout ends. Stack the concrete blocks so that the container is level, sturdy and won't tip over. You'll most likely need about four blocks so that you can stack them and raise the container about 2' off the ground, which will make it easier to retrieve water.