I have an asphalt roof. I have metal gutters and downspouts. I installed a 3 55 gallon food grade plastic barrel system with a black plastic y in 3" upright over my downspout I cut in half. I slipped the y over the downspout and filled it in with foam spray in insulation. The bottom of the y has a screw in plug. and is about 2' from top to bottom the 1" y goes up then over to one of my barrels. Then I installed a pvc manifold at the bottom tieing all 3 barrels together and put a faucet in the center. They all equal out and fill together. The purpose of the y at the bottom of the downspout is the heavy impuritys drop to the plug at the bottom like gravel and leaves and dirt off the roof and clean water rises to the y and into the tanks. I then filter the collected water in a bucket filter system using a berkey black filter. Whenever I want drinking water I just take a clean milk jug or two out and fill them up and transfer to the berkey bucket system. I have cut my water bill in half and have 165 gallon capacity and can add more barrels whenever I wish. When the city water supply runs out I will still have drinking water for a couple months if it does not rain. If it does rain there could be enough to even flush the toilet and wash a few clothes and dishes. Best move I have made in a while.