Contamination of potable roof-collected rainwater in Auckland, New Zealand

Abstract

One-hundred and twenty-five domestic roof-collected rainwater supplies in four rural Auckland districts were investigated in a cross-sectional survey to determine water quality. Samples of cold faucet water were analysed for physico-chemical and microbiological determinands, including metals (zinc, copper and lead), bacterial indicator organisms—heterotrophic plate count (HPC), total coilforms (TC), faecal coliforms (FC), enterococci (ENT), bacterial pathogens including Salmonella spp., Legionella spp., Campylobacter spp., Aeromonas spp. and the protozoa, Cryptosporidium and Giardia. Twenty-two supplies (17.6%) exceeded one or more of the maximum acceptable values (MAV) or maximum guideline values for chemical determinands of the New Zealand Drinking Water Standards (NZDWS) and 70 (56.0%) supplies exceeded the microbiological criteria of <1 FC/100 mL. Eighteen supplies (14.4%) exceeded the NZDWS MAV for lead of 0.01 mg/L and three (2.4%) exceeded that for copper, of 2 mg/L. Those supplies with lead or galvanised iron comprising part of the roof or collecting system were more likely to show lead contamination ( p=0.019) as were those supplies with a pH less than 7 ( p=0.013). The presence of the indicator organisms HPC, TC, FC and ENT were all significantly correlated with one another. Aeromonas spp. were identified in 20 (16.0%) supplies. There was a positive association between the presence of Aeromonas and the bacterial indicator organisms. Households reporting at least one member with gastrointestinal symptoms in the month prior to sampling, were more likely to have Aeromonas spp. identified in their water supply than those households without symptoms (odds ratio 3.22, 95% CI 1.15–9.01, p=0.021). Salmonella typhimurium was detected in one of 115 (0.9%) supplies. Legionella spp. and Campylobacter spp. were not detected. There were 50 supplies sampled for protozoa (sampling criteria: ≥30 FC or ≥60 ENT). Cryptosporidium oocysts were detected in 2 (4%) of these. Giardia was not detected. This study demonstrates that roof-collected rainwater systems provide potable supplies of relatively poor physicochemical and microbiological quality in the Auckland area. Further research is required on Aeromonas spp . as potential indicators of both microbiological quality and health risk along with design and maintenance strategies to minimise contamination of potable roof-collected rainwater supplies.