Assessment of First Flush Roof Runoff Water Quality: A Case Study in Southern Brazil

Rainwater harvesting systems may supply users with contaminated water if certain precautions are not taken. This study aims to quantify the levels of total coliforms and Escherichia. coli in rainwater at the beginning of runoff from a fibre cement roof located in Florianópolis, southern Brazil. Samples of roof runoff were collected, and physical–chemical parameters were quantified in addition to the microbiological ones. Finally, the existence of a possible correlation between these parameters was assessed. The results of laboratory tests were statistically described and submitted to correlation analysis. The analyses showed the existence of total coliforms in 100% of the samples and that E. coli can highly contaminate the roof runoff once some samples reach the test's detection limit (2419.6 NMP/100 mL). Furthermore, correlations between E. coli and the parameters pH, turbidity and apparent colour were observed. The study shows the importance of using first flush devices or techniques for rainwater treatment in rainwater harvesting systems to reduce users’ health risks.