Preliminary Roof Runoff Water Quality Results for the Miami Portion of the "Off the Roof" Citizen Science Project

Increasing demand for water creates a need to seek alternative water sources. One possible solution is to use roof runoff as a source. Roof runoff has been widely used in past and present times, but there is limited information concerning its microbial characterization. To address this data gap, a citizen science project aimed at collecting data on roof runoff from urban/suburban areas in four different US cities (Baltimore, Tucson, Fort Collins, and Miami) was designed. Additional goals of this project are to collect data that helps to address water treatment needs and to motivate the public to participate in practical science and research projects that may impact their communities. The Miami portion of the project consisted of seven participants who were provided with two 55-gallon rain barrels and supplies needed to connect them to downspouts in order to collect three seasonal samples (summer, fall, and winter) during 2018-2019. Volunteers were reminded to have the barrels ready (empty and rinsed) for water sampling before each potential rain event. Each event collected 3, 1-gallon and 1, 1-liter samples. The 1-gallon samples were filtered in the lab using dead end ultrafiltration, and the filters with residues were sent to the Environmental Protection Agency for quantification of bacterial and protozoan pathogens. The 1-L samples were sent to Colorado State University for physical-chemical and biological analyses.

The results yielded total coliform ranges of log₁₀ [most probable number (MPN)/ 100 milliliter (ml)] 2.7-3.0 for Summer, 2.6-3.0 (Fall), and 2.2-3.0 (Winter). Similarly, seasonal values of E. coli in log₁₀ MPN/100 ml are in the range of 0-1.9, 0-2.8, and 0-3.0. Enterococci seasonal ranged from 1.4-3.0, 2.1-3.0 and 2.5-3.0 respectively. Seasonal Chemical Oxygen Demand (COD) was in the range of 0-62, 12-170, and 9-110.5 mg/L, and turbidity was 1-40, 3-85.5 and 3-55 NTU, correspondingly.

Based on California reclaimed water irrigation standards of total coliforms 0.34 log₁₀ MPN/ 100 ml and Texas standards for E. coli of 1.3, roof runoff could be an alternative water source for irrigation though treatment would be required. These preliminary findings highlight the need for continuing study of roof runoff water quality to address its viability as an alternative source and possible treatment requirements.