Harvesting rainwater for drinking in urban areas – What is being consumed?

Increased use of alternative water sources may help bridge the disparity between demand for and sufficient supplies of safe water. Rainwater harvesting is one approach with the potential to reduce potable water consumption. However there are public health concerns surrounding its use for drinking, particularly regarding the highly variable quality that may not comply with drinking water guidelines. This study assessed the microbiological quality of rainwater used primarily for drinking in urban Australia. Samples collected at weekly, 4-weekly and quarterly intervals over 1 year were analysed for indicator organisms – E. coli, total coliforms, Enterococcus; and Heterotrophic Plate Count (HPC) and pathogens using standard methods. Data were analysed to determine the relationship between microbiological quality, season, rainfall, rainwater system parameters, and implementation of recommended maintenance strategies. The prevalence of Salmonella was low (0.3%) and human pathogenic strains of Campylobacter, Giardia, and Cryptosporidium were not detected, however the overall microbiological quality was poor when compared with drinking water standards. Bacterial indicator levels varied over the sampling period, with greater bacterial load in winter, and higher heterotrophic plate counts (HPC) 24h and 48h after rainfall events. Comparison of the recommended maintenance strategies showed that when four or five of strategies were implemented HPC was significantly lower compared with tanks where none or one strategy was implemented. While this study was unable to relate water quality data with health outcomes in consumers, the highly variable microbiological quality may present a health risk. Consumers should implement and adhere to recommended maintenance strategies to ensure optimal rainwater quality.