Assessment of water quality of first-flush roof runoff and harvested rainwater

Abstract

Summary Six pilot rainwater harvesting systems were installed in five urban, suburban and rural houses, and on a university campus. The systems consist of horizontal gutters to collect roof drainage, and downdrains which end into one or two plastic storage tanks. Devices were also provided to remove first-flush water. Water quality was monitored in the storage tanks and the first-flush devices during the 2-year period from October 2006 to November 2008. Water samples were collected at a frequency of once every 10 days, and analyzed according to potable water specifications to determine major anions (e.g., SO 4 2 - , NO 3 - , NO 2 - , F−, Cl−) and cations (e.g., NH 4 + , Na+, K+, Ca2+, Mg2+), total suspended solids, alkalinity, total phosphorus and microbiological indicators (e.g., total coliforms, Escherichia coli, Streptococcus, Clostridium perfrigens, Pseudomonas syringae and total viable counts at 22 °C and 37 °C). Furthermore, temperature, pH, dissolved oxygen and electrical conductivity were measured in situ. The mean concentrations of chemical parameters in harvested rainwater (with the exception of NH 4 + ) were below the limits set by the 98/93/EU directive for drinking water. Total coliforms were detected in 84.4–95.8% of the collected rainwater samples in the six tanks. E. coli, Streptococcus, C. perfrigens, P. syringae and total viable counts at 22 °C and 37 °C were found at low counts in samples of collected rainwater. The collected rainwater quality was found satisfactory regarding its physicochemical parameters, but not regarding its sanitary quality. Therefore, rainwater harvesting systems in this area could only supply water appropriate for use as gray water.