Rainwater harvesting/Rainwater harvesting system/Rainwater collection surface

The collection surface is the element of a rainwater harvesting system where rain impacts an area and directed, usually via gravity, to storage or overflow. The below discussed roofing surfaces are categorized by their material compositions and combinations and common design in built structures. A treatment is given to first the materials that form the bulk of the roofing material or if more significant, the outermost layer.

Composite Shingle
Durable. Asphalt mixture with an reinforcing mixture such as fiber glass, and a mineral topping for UV protection. Due to mineral aggregation and flaking, asphalt shingle roofs are no recommended for potable water rainwater harvesting systems.

Corrugated Asphalt Panel
Formed corrugated panel made of asphalt, a reinforcing fiber and topped with painted or coated surface. Due to presence of asphalt, use for potable water is not recommended. However this only happens if the outer surface is cracked or broken in some to allow water access to the underside.

Tile
Overlapping pieces of tile can be a common roofing surface in dryer and more arid regions of the world. Depending on the methods used for manufacturing, the water that comes off this roof can be used for potable purposes.

Wood
As long as the wood is not treated with a harsh fire retardant or other kinds of chemical that can leach over time into water, rainwater from wood shingles is potentially safe for potable use.

Polyvinyl and Vinyl
Polyvinyl and vinyl are commonly used clear plastic surfaces used to house sunrooms, patios and greenhouses. This is generally considered safe for potable use.

Green Roof
Much more consideration during the design process must be given to the kind and amount of pollutants particulates that will wash off from a green roof into the collection system.

Metal
Can either be standing seam or corrugated. Metal, depending on type, is usually galvanized or painted for protection against the elements (to prevent rust). Extra consideration must be given for older metal roofs or metal roofing with questionable manufacturing techniques.

Built Up Flat Roof
Common roof in the southwestern US and other arid areas. Composite of decking overlaid by water proofing surfaces such as felt paper, tar, and usually finished with a rubber surfacing or other plastic type membrane for water proofing. Not recommended for potable water uses, due to risk of contamination from layers under the rubber or elastomeric membranes.