Unpainted galvanized metal roofing is the best catchment surface for potable-water systems because it's smooth and nontoxic. Clay or concrete tile and slate also work well. Asphalt, asbestos, chemically treated wood shingles, and some painted metal roofs, however, can leach toxic materials and are recommended only for nonpotable water uses.
As in a simple system, gutters and downspouts should have leaf screens. But it's important that those gutters not have lead solder or lead-based paints. Seamless aluminum and vinyl gutters are fine. Also, a roof washer, a filtration system that removes any remaining leaves, debris, and bird droppings, should be placed in the line before the water enters a storage tank.
Shown: Before the water empties into the tanks, a primary filter called a roof washer helps remove leaves and other large debris.