While it is possible to harvest rainwater from surfaces other than above-ground roofs, such as patios, lawns, gardens, driveways, roadways, parking garages and parking lots, these surfaces are not suitable catchments for rainwater harvesting systems because of water quality concerns. Water collected from such surfaces may be contaminated with fertilizer, herbicides, fecal matter, garbage, oil or chemicals.
The outdoor environment in the local area of the building site, including its immediate surroundings, should be investigated to identify contaminants that could adversely affect the quality of the non-potable water delivered by the rainwater harvesting system. Contaminants of concern include industrial and urban traffic emissions, and pesticides and other agricultural chemicals. Other factors that can influence the levels of contaminants in the delivered non-potable water include the building’s geometry, and prevailing winds and seasonal activity in the local area. Design features should be incorporated in the rainwater harvesting system to mitigate the risks associated with any identified contaminants of concern.