Rainwater samples were collected from rainwater harvesting (RWH) systems at seven sites located in a 30 km radius around the City of Guelph in Ontario, Canada. From October 2006 to October 2007, a total of 360 samples were collected from two sampling locations—the rainwater cistern and at the point of use—and analysed for pH, turbidity, colour, total and fecal coliforms, total organic carbon, total nitrogen and UV absorbance (254 nm). Additional parameters, including polycyclic aromatic hydrocarbons, total metals, Campylobacter and Legionella were examined in selected samples. Following data collection, statistical analysis was performed to investigate the factors that influenced rainwater quality. The results of the quality assessment programme were largely consistent with those reported by several other researchers, with the exception of improved microbiological quality during periods of cold weather. Total and fecal coliforms were detected in 31% and 13% of the rainwater samples, respectively, while neither Campylobacter nor Legionella were detected above 1 CFU/100 ml detection limits. The results indicate that, while quality can be expected to vary with environmental conditions, the rainwater from a RWH system can be of consistently high quality through the selection of appropriate catchment and storage materials and the application of post-cistern treatment.

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