Rainwater Harvesting for Non-Potable Use in Gardens: A Comparison of Runoff Water Quality from Green vs. Traditional Roofs

Sustainable stormwater management involves ensuring that site runoff not exceed the pre-development peak flow rate and volume, typically accomplished through the use of water retention, infiltration, and reuse onsite through rainwater harvesting. Certain roofing materials, however, may be a pollutant source, thus, influencing the runoff's potential for harvesting. This project focuses on the first year of roof life for several traditional roofs and an extensive green roof. Substantial and significant releases of zinc and copper originated from an uncoated galvanized roof and from two treated woods, respectively. Roof runoff concentrations during early life indicated potential toxicity concerns for zinc and copper both in the water and from the potential buildup in the soil. Periodic elevated nutrient concentrations also were seen. Additionally, periodic spikes in pollutant concentrations after periods of low water concentrations indicated that elevated pollutant levels simply were not a result of washoff from excess preservative remaining on the surface of the material at installation.