An inch of rain puts about 600 gallons of water atop a 1,000-square-foot house. Rain gutters capture it; from a downspout, you can direct it into a cistern to help water your garden.
At Islandwood Environmental Learning Center on Bainbridge Island, Washington, three steel cisterns store rainwater from a nearby roof. By the time vegetables start growing in spring, the tanks are full and the water travels through a gravity-fed drip system to irrigate crops.
INFO Pictured cisterns are from Texas Metal Cisterns ($380 for 200-gallon size to $1,070 for 1,200-gallon size;