Rainwater Collection
Source: Wikimedia Commons


Rainwater Harvesting Collection Surfaces

A lot of people ask what type of material is suitable for rainwater harvesting.  While a metal roof is ideal, especially for drinking water, most any material can be used.  Wood and clay tile roof shingles are the least desirable because the porous surface harbors microbes, but if the water is for secondary use, they don’t present a problem.  Concrete and asphalt paving and even brick or porous pavement as well as turf can be used to catch runoff.


The only roof material that has been approved by the National Sanitation Foundation (NSF) for potable systems is galv-alum (also called zinc-alum) steel.  Some seamless aluminum gutter systems with factory applied polyester coating have been approved as well.  All other roof materials have been used although it may be wise to treat the water before you drink it.

Composition shingles do not contribute appreciable amounts of hydrocarbons to the water after six months in the sun.  It is recommended that activated carbon (GAC) filtration be used for water collected from built-up hot tar roofs with rock ballast.  For secondary uses, anything goes.  If water quality is important to you, go with metal.

Impervious Surfaces 

Rain from concrete or asphalt pavement is called storm water runoff and is required by the EPA to be detained and treated, if necessary, before releasing into the environment.  This is increasingly being enforced now that the National Pollution Discharge Elimination System (NPDES) permits are required for most commercial and industrial facilities.

A lot of hydrocarbon and animal feces are present on ground level surfaces, so it is not prudent to use storm water indoors.  It can be treated with bio-swales and sand filter beds to secondary standards, but typically it is used only for tertiary uses like irrigating ornamental plants, shade trees and rain gardens.  It can be collected in a pond and infiltrated but it probably would not be suitable for fish or even stock ponds unless the water was sent through a series of retention ponds where natural bio-remediation could occur first.

Storm water is a source of non-point source pollution and should be allowed to settle out sediment and trickle through a sand bed or other filter media before reuse.  Underground storage is best since it would otherwise be necessary to pump the water.

Pervious Surfaces 

Pervious pavement like recycled brick, concrete pavers, GravelPave ™ or GrassPave ™ grid systems, green roofs and turf can yield useful amounts of runoff and, when combined with underground modular storage systems, are a good source of clean irrigation water.

With impervious surfaces being tightly regulated, there is a trend to these paving methods more and more.  This water should not be delivered to a piped sewer to be conveyed off the property upon which it fell.  That would break the natural hydro-logic cycle and impact the aquifer.

Every aquifer in the country, and probably most if not all, in the world are being depleted faster than nature’s ability to replenish them.  Use storm water for irrigation, infiltration, vehicle washing and soil storage, not toilet flushing or clothes washing.