Metals in Rooftop Harvested Rainwater

Pilot-scale metal roof donated and constructed by Ja-Mar Roofing

Carolina B. Mendez, Brigit R. Afshar, Kerry Kinney, Michael E. Barrett, Mary Jo Kirisits

Department of Civil, Architectural, and Environmental Engineering, The University of Texas at Austin

Rainwater harvesting systems are widely being considered to meet current and future water demands. To insure the potability of rainwater harvesting systems, roofing materials need to be carefully selected in order to minimize contaminants in the roof-runoff. In this study, rooftop harvested rainwater was analyzed from five pilot-scale roofs and three full-scale residential roofs. Various microbial and chemical constituents were analyzed in the “first flush” and water after the first flush. The chemical constituents included nine metals that were analyzed by ICP-MS. All metal concentrations decreased after the first flush, indicating that harvested rainwater quality improves with roof flushing. Out of the nine metals tested, Fe and Al concentrations in the harvested rainwater after the first flush exceeded USEPA secondary MCLs for drinking water. As a result, to insure the potability of harvested rainwater, it is recommended that a first flush diverter and additional treatment should be implemented to reduce contaminants.

Mendez, C. B., J. B. Klenzendorf, B. R. Afshar, M. T. Simmons, M. E. Barrett, K. A. Kinney, and M. J. Kirisits. (2011) “The Effect of Roofing Material on the Quality of Harvested Rainwater.” Water Research 45:5:2049-2059.